newb: comapring two strings

[John Machin]

> Use the levenshtein distance.

Given the constraint that the two strings are the same length, I'm
assuming (as other posters appear to have done) that "vary by only one
character" precludes insertion and deletion operations.

In that case, the problem can be solved in O(n) time by a simple loop
which counts the number of differences and notes the position of the
first (if any) difference. Any full-distance Levenshtein method that
does no pre-processing must take O(n**2) time. It is possible to take
advantage of the fact that the OP doesn't care about what the distance
is exactly if it is not 1; 0 is just as bad as 2, 3, 4, etc. In this
case it is possible to achieve O(n) time [ref. Ukkonen]. However (a)
one still needs to track where the difference arose (b) we are talking
about extreme overkill for the OP's problem.