Match sub-string within a string with tolerance of 1 character mismatch

Question

I was going through some Amazon interview questions on CareerCup.com, and I came across this interesting question which I haven\'t been able to figure out how to do. I have

Answer 1

Is the problem to do this efficiently?

The naive solution is to loop over every substring of size substr in str, from left to right, and return true if the current substring if only one of the characters is different in a comparison.

Let n = size of str Let m = size of substr

There are O(n) substrings in str, and the matching step takes time O(m). Ergo, the naive solution runs in time O(n*m)