16.计算最接近目标值的和

3Sum Closest

问题描述：

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).

测试代码（c++)：

int threeSumClosest(vector<int>& nums, int target) {        int sum = 0,result = 0, gap = 9999;        sort(nums.begin(),nums.end());        for(int i=0;i<nums.size()-1;i++)        {            int j = i+1;            int k = nums.size()-1;            while(j<k)            {                sum = nums[i]+nums[j]+nums[k];                if(abs(sum-target)<gap)                {                    result = sum;                    gap = abs(sum-target);                }                if(sum<target)                {                    j++;                }else if(sum>target)                {                    k--;                }else {                    return sum;                }            }        }        return result;     }

性能：