Problem 317. Find the stride of the longest skip sequence

Created by Ned Gulley

Solve Later

{"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":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>We define a</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:i/></w:rPr><w:t>skip sequence</w:t></w:r><w:r><w:t> as a regularly-spaced list of integers such as might be generated by MATLAB's</w:t></w:r><w:r><w:t> </w:t></w:r><w:hyperlink w:docLocation=\"http://www.mathworks.com/help/matlab/ref/colon.html\"><w:r><w:t>colon operator</w:t></w:r></w:hyperlink><w:r><w:t>. We will call the inter-element increment the</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:i/></w:rPr><w:t>stride</w:t></w:r><w:r><w:t>. So the vector 2:3:17 or [2 5 8 11 14 17] is a six-element skip sequence with stride 3.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Given the vector a, your job is to find the stride associated with the longest skip sequence you can assemble using any of the elements of a in any order. You can assume that stride is positive and unique.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Example:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ input  a = [1 5 3 11 7 2 4 9]\n output stride is 2]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>since from the elements of a we can build the six-element sequence [1 3 5 7 9 11].</w:t></w:r></w:p></w:body></w:document>"},{"partUri":"/matlab/output.xml","contentType":"text/xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?><embeddedOutputs><metaData><evaluationState>manual</evaluationState><layoutState>code</layoutState><outputStatus>ready</outputStatus></metaData><outputArray type=\"array\"/><regionArray type=\"array\"/></embeddedOutputs>"}]}

Solve

Solution Stats

907 Solutions
145 Solvers

Last Solution submitted on Aug 20, 2023

Last 200 Solutions

Problem Comments

4 Comments

4 Comments

Show 1 older comment

@bmtran (Bryant Tran) on 13 Feb 2012

this problem is multi-valued. it is equally valid to say that, in the case of the example, the stride associated with the longest skip sequence is -2.

Ned Gulley on 14 Feb 2012

Fair enough. I changed the wording to remove the ambiguity.

Ned Gulley on 13 Feb 2014

I added another test and rescored. It appears that DIST no longer works. The DIST function is from the Neural Networks Toolbox. It shouldn't have worked in the past, but since it did, it played a part in a lot of answers. Sorry for the discontinuity.

Jean-Marie Sainthillier on 28 Jan 2015

Tough !
Two years before understand that the sequence must contain only elements of a :)

Solution Comments

Show comments

Problem Recent Solvers145

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Problem 317. Find the stride of the longest skip sequence

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers145

Suggested Problems

More from this Author50

Problem Tags

Community Treasure Hunt

Problem 317. Find the stride of the longest skip sequence

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers145

Suggested Problems

More from this Author50

Problem Tags

Community Treasure Hunt

Players