Algorithm to determine if array contains n…n+m?

Question

I saw this question on Reddit, and there were no positive solutions presented, and I thought it would be a perfect question to ask here. This was in a thread about interview

Answer 1

The Answer from "nickf" dows not work if the array is unsorted var_dump(testArray(array(5, 3, 1, 2, 4), 1, 5)); //gives "duplicates" !!!!

Also your formula to compute sum([n...n+m-1]) looks incorrect.... the correct formula is (m(m+1)/2 - n(n-1)/2)