3Sum Closest问题及解法

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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.

示例：

 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).

问题分析：

要求三个数的和最接近目标值，可分为以下几个步骤：

1.将数组升序排序

2.设置两个指针 front 和 back 分别指向数组的前段和后端

3.先选取好第一个元素，然后遍历第二和第三个元素，将三者的和与目标值target作比较，选取距离较近的

过程详见代码：

class Solution {
public:int threeSumClosest(vector<int>& nums, int target) {int res = 0;int dist = INT_MAX;sort(nums.begin(), nums.end());//排序 for(int i = 0; i < nums.size(); i++){int front = i + 1;int back = nums.size() - 1;while(front < back){int sum = nums[i] + nums[front] + nums[back];if(sum < target) {int temp = target - sum;if(temp < dist){dist = temp;res = sum;}front++;}else if(sum > target){int temp = sum - target;if(temp < dist){dist = temp;res = sum;}back--;}else{return target;}}}return res;}
};

问题难度不大，有疑问的话欢迎交流~~

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