3 Sum Closest

Given an array S of n integers, find three integers in S such that the
sum is closest to a given number, target. Return the sum of the three
integers. You may assume that each input would have exactly one
solution.

For example, given array S = {-1 2 1 -4}, and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).