16. 3Sum Closest 解题记录

题目描述：

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).

解题思路：

本题我的思路借鉴了上一题的3Sum的思路：先将数组进行排序，再将头一个数固定，这个数以下的数组从左右两端开始搜索，每次都将得到的值进行比较。

代码：

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