{"group":{"id":1,"name":"Community","lockable":false,"created_at":"2012-01-18T18:02:15.000Z","updated_at":"2025-12-14T01:33:56.000Z","description":"Problems submitted by members of the MATLAB Central community.","is_default":true,"created_by":161519,"badge_id":null,"featured":false,"trending":false,"solution_count_in_trending_period":0,"trending_last_calculated":"2025-12-14T00:00:00.000Z","image_id":null,"published":true,"community_created":false,"status_id":2,"is_default_group_for_player":false,"deleted_by":null,"deleted_at":null,"restored_by":null,"restored_at":null,"description_opc":null,"description_html":null,"published_at":null},"problems":[{"id":1826,"title":"Find vampire numbers","description":"A vampire number is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\r\nat most one of x and y are divisible by 10;\r\nx and y have the same number of digits; and\r\nThe digits in v consist of the digits of x and y (including anyrepetitions).\r\nIf these conditions are met, x and y are known as \"fangs\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\r\nWrite a function that returns all the vampire numbers in a given array. The output is a vector.\r\nExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\r\nSee also:  Problem 1825. Find all vampire fangs and Problem 1804. Fangs of a vampire number.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.4333px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 265.3px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 406.5px 132.65px; transform-origin: 406.5px 132.65px; vertical-align: baseline; \"\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 21px; text-align: left; transform-origin: 383.5px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 5.025px 7.81667px; transform-origin: 5.025px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eA\u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003evampire number\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 307.642px 7.81667px; transform-origin: 307.642px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003col style=\"block-size: 61.3px; counter-reset: list-item 0; font-family: Helvetica, Arial, sans-serif; list-style-type: decimal; margin-block-end: 20px; margin-block-start: 10px; margin-bottom: 20px; margin-top: 10px; perspective-origin: 390.5px 30.65px; transform-origin: 390.5px 30.65px; margin-top: 10px; margin-bottom: 20px; \"\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 134.558px 7.81667px; transform-origin: 134.558px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eat most one of x and y are divisible by 10;\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 142.933px 7.81667px; transform-origin: 142.933px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003ex and y have the same number of digits; and\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 228.358px 7.81667px; transform-origin: 228.358px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eThe digits in v consist of the digits of x and y (including anyrepetitions).\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 21px; text-align: left; transform-origin: 383.5px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 383.5px 7.81667px; transform-origin: 383.5px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eIf these conditions are met, x and y are known as \"fangs\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 294.242px 7.81667px; transform-origin: 294.242px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eWrite a function that returns all the vampire numbers in a given array. The output is a vector.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 215.517px 7.81667px; transform-origin: 215.517px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 32.9417px 7.81667px; transform-origin: 32.9417px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eSee also: \u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003eProblem 1825. Find all vampire fangs\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 13.9583px 7.81667px; transform-origin: 13.9583px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e and\u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003eProblem 1804. Fangs of a vampire number\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function y =find_vampire(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nfiletext = fileread('find_vampire.m');\r\nillegal = contains(filetext, 'assignin') || contains(filetext, 'regexp') ...\r\n    || contains(filetext, '1260') || contains(filetext, 'intersect') ;\r\n%test case enhanced on 01-08-2024\r\n%intersect and the elements themselves were used to hard-code the problem\r\nassert(~illegal)\r\n\r\n%%\r\nx = 1000:2000;\r\nv = find_vampire(x);\r\nv_correct = [1260 1395 1435 1530 1827];\r\nassert(isequal(v,v_correct))\r\n\r\n%%\r\nx = 1:999;\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = reshape(2000:2999,100,[]);\r\nv = find_vampire(x);\r\nv_correct = 2187;\r\nassert(isequal(v,v_correct))\r\n\r\n%%\r\nx = [];\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = -2000:-1000;\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = 125000:125501;\r\nv = find_vampire(x);\r\nv_correct = [125248 125433 125460 125500];\r\nassert(isequal(v,v_correct))","published":true,"deleted":false,"likes_count":12,"comments_count":7,"created_by":1011,"edited_by":223089,"edited_at":"2024-08-01T16:28:29.000Z","deleted_by":null,"deleted_at":null,"solvers_count":394,"test_suite_updated_at":"2024-08-01T16:28:29.000Z","rescore_all_solutions":false,"group_id":8,"created_at":"2013-08-14T22:41:30.000Z","updated_at":"2026-02-15T13:30:53.000Z","published_at":"2013-08-14T22:42:12.000Z","restored_at":null,"restored_by":null,"spam":null,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003evampire number\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eat most one of x and y are divisible by 10;\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003ex and y have the same number of digits; and\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eThe digits in v consist of the digits of x and y (including anyrepetitions).\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eIf these conditions are met, x and y are known as \\\"fangs\\\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eWrite a function that returns all the vampire numbers in a given array. The output is a vector.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eSee also: \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eProblem 1825. Find all vampire fangs\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e and\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eProblem 1804. Fangs of a vampire number\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"},{"id":1394,"title":"Prime Ladders","description":"A \u003chttp://en.wikipedia.org/wiki/Word_ladder word ladder\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\r\n\r\n COLD\r\n CORD\r\n CARD\r\n WARD\r\n WARM\r\n\r\nA number ladder does much the same thing, changing one digit at a time. A *prime ladder* is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\r\n\r\n 757 \r\n 157\r\n 137\r\n 139\r\n\r\nGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element. \r\n\r\nTo restate the above example, consider\r\n\r\n p1 = 757\r\n p2 = 139\r\n\r\nfor which an acceptable answer is\r\n\r\n ladder = [757; 157; 137; 139]\r\n\r\nYou can assume that p1 and p2 contain the same number of digits. I am not looking for a unique answer. I will only check that the conditions of a prime ladder are met.\r\n\r\n","description_html":"\u003cp\u003eA \u003ca href = \"http://en.wikipedia.org/wiki/Word_ladder\"\u003eword ladder\u003c/a\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\u003c/p\u003e\u003cpre\u003e COLD\r\n CORD\r\n CARD\r\n WARD\r\n WARM\u003c/pre\u003e\u003cp\u003eA number ladder does much the same thing, changing one digit at a time. A \u003cb\u003eprime ladder\u003c/b\u003e is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\u003c/p\u003e\u003cpre\u003e 757 \r\n 157\r\n 137\r\n 139\u003c/pre\u003e\u003cp\u003eGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element.\u003c/p\u003e\u003cp\u003eTo restate the above example, consider\u003c/p\u003e\u003cpre\u003e p1 = 757\r\n p2 = 139\u003c/pre\u003e\u003cp\u003efor which an acceptable answer is\u003c/p\u003e\u003cpre\u003e ladder = [757; 157; 137; 139]\u003c/pre\u003e\u003cp\u003eYou can assume that p1 and p2 contain the same number of digits. I am not looking for a unique answer. I will only check that the conditions of a prime ladder are met.\u003c/p\u003e","function_template":"function ladder = prime_ladder(p1,p2)\r\n  ladder = 0;\r\nend","test_suite":"%%\r\n\r\np1 = 13;\r\np2 = 29;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 389;\r\np2 = 269;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 761;\r\np2 = 397;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 983;\r\np2 = 239;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 271;\r\np2 = 439;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 877;\r\np2 = 733;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 2267;\r\np2 = 1153;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n","published":true,"deleted":false,"likes_count":10,"comments_count":3,"created_by":7,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":55,"test_suite_updated_at":"2013-03-27T21:24:26.000Z","rescore_all_solutions":false,"group_id":1,"created_at":"2013-03-26T22:51:16.000Z","updated_at":"2026-01-03T14:28:57.000Z","published_at":"2013-03-27T15:28:59.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"targetMode\":\"\",\"relationshipId\":\"rId1\",\"target\":\"/matlab/document.xml\"},{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/output\",\"targetMode\":\"\",\"relationshipId\":\"rId2\",\"target\":\"/matlab/output.xml\"}],\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"relationship\":[],\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\\n\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"http://en.wikipedia.org/wiki/Word_ladder\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eword ladder\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ COLD\\n CORD\\n CARD\\n WARD\\n WARM]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA number ladder does much the same thing, changing one digit at a time. A\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:rPr\u003e\u003cw:b/\u003e\u003c/w:rPr\u003e\u003cw:t\u003eprime ladder\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ 757 \\n 157\\n 137\\n 139]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eTo restate the above example, consider\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ p1 = 757\\n p2 = 139]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003efor which an acceptable answer is\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ ladder = [757; 157; 137; 139]]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eYou can assume that p1 and p2 contain the same number of digits. I am not looking for a unique answer. I will only check that the conditions of a prime ladder are met.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\"},{\"partUri\":\"/matlab/output.xml\",\"contentType\":\"text/xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\" standalone=\\\"no\\\" ?\u003e\u003cembeddedOutputs\u003e\u003cmetaData\u003e\u003cevaluationState\u003emanual\u003c/evaluationState\u003e\u003clayoutState\u003ecode\u003c/layoutState\u003e\u003coutputStatus\u003eready\u003c/outputStatus\u003e\u003c/metaData\u003e\u003coutputArray type=\\\"array\\\"/\u003e\u003cregionArray type=\\\"array\\\"/\u003e\u003c/embeddedOutputs\u003e\"}]}"}],"problem_search":{"errors":[],"problems":[{"id":1826,"title":"Find vampire numbers","description":"A vampire number is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\r\nat most one of x and y are divisible by 10;\r\nx and y have the same number of digits; and\r\nThe digits in v consist of the digits of x and y (including anyrepetitions).\r\nIf these conditions are met, x and y are known as \"fangs\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\r\nWrite a function that returns all the vampire numbers in a given array. The output is a vector.\r\nExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\r\nSee also:  Problem 1825. Find all vampire fangs and Problem 1804. Fangs of a vampire number.","description_html":"\u003cdiv style = \"text-align: start; line-height: 20.4333px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: rgb(0, 0, 0); white-space: normal; \"\u003e\u003cdiv style=\"block-size: 265.3px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 406.5px 132.65px; transform-origin: 406.5px 132.65px; vertical-align: baseline; \"\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 21px; text-align: left; transform-origin: 383.5px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 5.025px 7.81667px; transform-origin: 5.025px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eA\u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003evampire number\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 307.642px 7.81667px; transform-origin: 307.642px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003col style=\"block-size: 61.3px; counter-reset: list-item 0; font-family: Helvetica, Arial, sans-serif; list-style-type: decimal; margin-block-end: 20px; margin-block-start: 10px; margin-bottom: 20px; margin-top: 10px; perspective-origin: 390.5px 30.65px; transform-origin: 390.5px 30.65px; margin-top: 10px; margin-bottom: 20px; \"\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 134.558px 7.81667px; transform-origin: 134.558px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eat most one of x and y are divisible by 10;\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 142.933px 7.81667px; transform-origin: 142.933px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003ex and y have the same number of digits; and\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli style=\"block-size: 20.4333px; counter-reset: none; display: list-item; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-start: 56px; margin-left: 56px; margin-top: 0px; perspective-origin: 362.5px 10.2167px; text-align: left; transform-origin: 362.5px 10.2167px; white-space-collapse: preserve; margin-left: 56px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-inline-start: 0px; margin-left: 0px; perspective-origin: 228.358px 7.81667px; transform-origin: 228.358px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eThe digits in v consist of the digits of x and y (including anyrepetitions).\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e\u003cdiv style=\"block-size: 42px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 21px; text-align: left; transform-origin: 383.5px 21px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 383.5px 7.81667px; transform-origin: 383.5px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eIf these conditions are met, x and y are known as \"fangs\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 294.242px 7.81667px; transform-origin: 294.242px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eWrite a function that returns all the vampire numbers in a given array. The output is a vector.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 215.517px 7.81667px; transform-origin: 215.517px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003cdiv style=\"block-size: 21px; font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 383.5px 10.5px; text-align: left; transform-origin: 383.5px 10.5px; white-space-collapse: preserve; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; \"\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 32.9417px 7.81667px; transform-origin: 32.9417px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003eSee also: \u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003eProblem 1825. Find all vampire fangs\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 13.9583px 7.81667px; transform-origin: 13.9583px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e and\u003c/span\u003e\u003c/span\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e \u003c/span\u003e\u003c/span\u003e\u003ca target='_blank' href = \"/#null\"\u003e\u003cspan style=\"\"\u003e\u003cspan style=\"\"\u003eProblem 1804. Fangs of a vampire number\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\u003cspan style=\"block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2.23333px 7.81667px; transform-origin: 2.23333px 7.81667px; unicode-bidi: normal; \"\u003e\u003cspan style=\"\"\u003e.\u003c/span\u003e\u003c/span\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","function_template":"function y =find_vampire(x)\r\n  y = x;\r\nend","test_suite":"%%\r\nfiletext = fileread('find_vampire.m');\r\nillegal = contains(filetext, 'assignin') || contains(filetext, 'regexp') ...\r\n    || contains(filetext, '1260') || contains(filetext, 'intersect') ;\r\n%test case enhanced on 01-08-2024\r\n%intersect and the elements themselves were used to hard-code the problem\r\nassert(~illegal)\r\n\r\n%%\r\nx = 1000:2000;\r\nv = find_vampire(x);\r\nv_correct = [1260 1395 1435 1530 1827];\r\nassert(isequal(v,v_correct))\r\n\r\n%%\r\nx = 1:999;\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = reshape(2000:2999,100,[]);\r\nv = find_vampire(x);\r\nv_correct = 2187;\r\nassert(isequal(v,v_correct))\r\n\r\n%%\r\nx = [];\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = -2000:-1000;\r\nv = find_vampire(x);\r\nassert(isempty(v))\r\n\r\n%%\r\nx = 125000:125501;\r\nv = find_vampire(x);\r\nv_correct = [125248 125433 125460 125500];\r\nassert(isequal(v,v_correct))","published":true,"deleted":false,"likes_count":12,"comments_count":7,"created_by":1011,"edited_by":223089,"edited_at":"2024-08-01T16:28:29.000Z","deleted_by":null,"deleted_at":null,"solvers_count":394,"test_suite_updated_at":"2024-08-01T16:28:29.000Z","rescore_all_solutions":false,"group_id":8,"created_at":"2013-08-14T22:41:30.000Z","updated_at":"2026-02-15T13:30:53.000Z","published_at":"2013-08-14T22:42:12.000Z","restored_at":null,"restored_by":null,"spam":null,"simulink":false,"admin_reviewed":false,"description_opc":"{\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003evampire number\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e is a number v that is the product of two numbers x and y such that the following conditions are satisfied:\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eat most one of x and y are divisible by 10;\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003ex and y have the same number of digits; and\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"ListParagraph\\\"/\u003e\u003cw:numPr\u003e\u003cw:numId w:val=\\\"2\\\"/\u003e\u003c/w:numPr\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eThe digits in v consist of the digits of x and y (including anyrepetitions).\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eIf these conditions are met, x and y are known as \\\"fangs\\\" of v. For example, 1260 is a vampire number because 1260 = 21*60, so 21 and 60 are the fangs.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eWrite a function that returns all the vampire numbers in a given array. The output is a vector.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eExample: disp(find_vampire(1000:2000) 1260 1395 1435 1530 1827\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003cw:jc w:val=\\\"left\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eSee also: \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eProblem 1825. Find all vampire fangs\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e and\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eProblem 1804. Fangs of a vampire number\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003c/w:body\u003e\u003c/w:document\u003e\",\"relationship\":null}],\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"target\":\"/matlab/document.xml\",\"relationshipId\":\"rId1\"}]}"},{"id":1394,"title":"Prime Ladders","description":"A \u003chttp://en.wikipedia.org/wiki/Word_ladder word ladder\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\r\n\r\n COLD\r\n CORD\r\n CARD\r\n WARD\r\n WARM\r\n\r\nA number ladder does much the same thing, changing one digit at a time. A *prime ladder* is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\r\n\r\n 757 \r\n 157\r\n 137\r\n 139\r\n\r\nGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element. \r\n\r\nTo restate the above example, consider\r\n\r\n p1 = 757\r\n p2 = 139\r\n\r\nfor which an acceptable answer is\r\n\r\n ladder = [757; 157; 137; 139]\r\n\r\nYou can assume that p1 and p2 contain the same number of digits. I am not looking for a unique answer. I will only check that the conditions of a prime ladder are met.\r\n\r\n","description_html":"\u003cp\u003eA \u003ca href = \"http://en.wikipedia.org/wiki/Word_ladder\"\u003eword ladder\u003c/a\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\u003c/p\u003e\u003cpre\u003e COLD\r\n CORD\r\n CARD\r\n WARD\r\n WARM\u003c/pre\u003e\u003cp\u003eA number ladder does much the same thing, changing one digit at a time. A \u003cb\u003eprime ladder\u003c/b\u003e is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\u003c/p\u003e\u003cpre\u003e 757 \r\n 157\r\n 137\r\n 139\u003c/pre\u003e\u003cp\u003eGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element.\u003c/p\u003e\u003cp\u003eTo restate the above example, consider\u003c/p\u003e\u003cpre\u003e p1 = 757\r\n p2 = 139\u003c/pre\u003e\u003cp\u003efor which an acceptable answer is\u003c/p\u003e\u003cpre\u003e ladder = [757; 157; 137; 139]\u003c/pre\u003e\u003cp\u003eYou can assume that p1 and p2 contain the same number of digits. I am not looking for a unique answer. I will only check that the conditions of a prime ladder are met.\u003c/p\u003e","function_template":"function ladder = prime_ladder(p1,p2)\r\n  ladder = 0;\r\nend","test_suite":"%%\r\n\r\np1 = 13;\r\np2 = 29;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 389;\r\np2 = 269;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 761;\r\np2 = 397;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 983;\r\np2 = 239;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 271;\r\np2 = 439;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 877;\r\np2 = 733;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n\r\n%%\r\n\r\np1 = 2267;\r\np2 = 1153;\r\nladder = prime_ladder(p1,p2);\r\n\r\nassert(all(isprime(ladder)))\r\nassert(iscolumn(ladder))\r\nassert(ladder(1)==p1)\r\nassert(ladder(end)==p2)\r\nassert(all(sum(diff(num2str(ladder))~=0,2)==1))\r\n","published":true,"deleted":false,"likes_count":10,"comments_count":3,"created_by":7,"edited_by":null,"edited_at":null,"deleted_by":null,"deleted_at":null,"solvers_count":55,"test_suite_updated_at":"2013-03-27T21:24:26.000Z","rescore_all_solutions":false,"group_id":1,"created_at":"2013-03-26T22:51:16.000Z","updated_at":"2026-01-03T14:28:57.000Z","published_at":"2013-03-27T15:28:59.000Z","restored_at":null,"restored_by":null,"spam":false,"simulink":false,"admin_reviewed":false,"description_opc":"{\"relationships\":[{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/document\",\"targetMode\":\"\",\"relationshipId\":\"rId1\",\"target\":\"/matlab/document.xml\"},{\"relationshipType\":\"http://schemas.mathworks.com/matlab/code/2013/relationships/output\",\"targetMode\":\"\",\"relationshipId\":\"rId2\",\"target\":\"/matlab/output.xml\"}],\"parts\":[{\"partUri\":\"/matlab/document.xml\",\"relationship\":[],\"contentType\":\"application/vnd.mathworks.matlab.code.document+xml\",\"content\":\"\u003c?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\"?\u003e\\n\u003cw:document xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\u003e\u003cw:body\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:hyperlink w:docLocation=\\\"http://en.wikipedia.org/wiki/Word_ladder\\\"\u003e\u003cw:r\u003e\u003cw:t\u003eword ladder\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:hyperlink\u003e\u003cw:r\u003e\u003cw:t\u003e transforms one word to another by means of single-letter mutations. So COLD can become WARM like so (there are often multiple solutions):\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ COLD\\n CORD\\n CARD\\n WARD\\n WARM]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eA number ladder does much the same thing, changing one digit at a time. A\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e \u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:rPr\u003e\u003cw:b/\u003e\u003c/w:rPr\u003e\u003cw:t\u003eprime ladder\u003c/w:t\u003e\u003c/w:r\u003e\u003cw:r\u003e\u003cw:t\u003e is a number ladder with the additional constraint that each element is a prime number. Here is a prime ladder that connects 757 and 139\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ 757 \\n 157\\n 137\\n 139]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eGiven two numbers p1 and p2, construct a prime ladder column vector in which p1 is the first element, p2 is the last element, and each successive row differs by exactly one digit from the preceding element.\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eTo restate the above example, consider\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ p1 = 757\\n p2 = 139]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003efor which an acceptable answer is\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"code\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[ ladder = [757; 157; 137; 139]]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\u003c/w:p\u003e\u003cw:p\u003e\u003cw:pPr\u003e\u003cw:pStyle w:val=\\\"text\\\"/\u003e\u003c/w:pPr\u003e\u003cw:r\u003e\u003cw:t\u003eYou can assume that p1 and p2 contain the same number of digits. 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