Problem 317. Find the stride of the longest skip sequence
We define a skip sequence as a regularly-spaced list of integers such as might be generated by MATLAB's colon operator. We will call the inter-element increment the stride. So the vector 2:3:17 or [2 5 8 11 14 17] is a six-element skip sequence with stride 3.
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.
Example:
input a = [1 5 3 11 7 2 4 9] output stride is 2
since from the elements of a we can build the six-element sequence [1 3 5 7 9 11].
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4 Comments
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.
Fair enough. I changed the wording to remove the ambiguity.
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.
Tough !
Two years before understand that the sequence must contain only elements of a :)
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