[Array]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).

方法：对数组先进行排序，然后利用Two Pointer的思想进行。时间复杂度O（n²）

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        int sum = nums[0]+nums[1]+nums[2];
        int min_diff = abs(target - sum);
        for(int i=0;i<nums.size()-2;i++){
            int left = i+1;
            int right = nums.size()-1;
            while(left<right){
                 int temp_sum = nums[i]+nums[left]+nums[right];
                 if(temp_sum==target)
                    return temp_sum;
                int temp_diff = abs(temp_sum-target);
                if(temp_diff<min_diff){
                     min_diff = temp_diff;
                     sum = temp_sum;
                }
                if(temp_sum<target)
                    left++;
                else
                    right--;
            }
        }
        return sum;

    }
};