Three Sum

Given an array S of n integers, are there elements a, b, c in S such
that a + b + c = 0? Find all unique triplets in the array which gives
the sum of zero.

Note:
Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤
b ≤ c)
The solution set must not contain duplicate triplets.
For example, given array S = {-1 0 1 2 -1 -4},

A solution set is:
(-1, 0, 1)
(-1, -1, 2)