Determine whether or not there exist two elements in Set S whose sum is exactly x - correct solution?

Question

Taken from Introduction to Algorithms

Describe a Θ(n lg n)-time algorithm that, given a set S of n integers and another integer x, determines whet

Answer 1

1. This is correct; your algorithm will run in O(n lg n) time.

2. There is a better solution: your logic for calculating diff is incorrect. Regardless of whether a[i] is greater than or less than val, you still need diff to be val - a[i].