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

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.

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

解題思路：與15題l類似，先確定一個數，然後雙指標法

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        if(nums.size()<3)
            return 0;
        int result=nums[0]+nums[1]+nums[2],resultmin=abs(result-target);
        for(int i=0;i<nums.size()-2;i++){
            while(i!=0&&nums[i]==nums[i-1])
                i++;
            int low=i+1,high=nums.size()-1;
            while(low<high){
                int temp=nums[i]+nums[low]+nums[high];
                if(abs(temp-target)<resultmin){
                    resultmin=abs(temp-target);
                    result=temp;
                }     
                if(resultmin==0)
                    break;
                else if(temp<target)
                    low++;
                else
                    high--;
            }
        }
        return result;
    }
};