[Leetcode]3Sum 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).

先将所有元素排序，然后再遍历所有组合。

class Solution {public:int threeSumClosest(vector<int> &num, int target) {sort(num.begin(), num.end());int sum = 0, result = 0;int distance = numeric_limits<int>::max();for (int i = 0; i < num.size(); i++){if (i > 0 && num[i] == num[i - 1]){continue;}int j = i + 1;int k = num.size() - 1;while (j < k){sum = num[i] + num[j] + num[k];if (sum == target){return sum;}if (sum < target){if ((target - sum) < distance){result = sum;distance = target - sum;}j++;}else{if ((sum - target) < distance){result = sum;distance = sum - target;}k--;}}}return result;}};