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.
给一个n个整数的整数数组S，在数组S中找到三个数，这三个数的和最接近给的数target，返回这个三个数的和。你可以认为输入一定有一个解
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).