http://discuss.techinterview.org/default.asp?interview.11.613896.3
http://en.wikipedia.org/wiki/3SUM
Given an unsorted array of integers. Find any three numbers satisfying following condition:
c = a+b
First, sort the array in O(nlogn).
For each element c of the array try to find two numbers a and b such that a+b = c.
Time complexity:
O(n) to find a+b = c in sorted array. (We can use two pointers and move them towards the middle)
Since we do this for each element. O(n^2).
