16. 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).

同 3Sum，先排序，后两边夹逼

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class Solution { public:     int threeSumClosest(vector<int>& nums, int target) {         int len = nums.size();         if (len < 3) return 0;         sort(nums.begin(), nums.end());         int sum = 0;         int leastdif = INT_MAX;         for (int i = 0; i < len - 2; i++) {             int l = i + 1, r = len - 1;               while (l < r) {                 int dif = fabs(nums[i] + nums[l] + nums[r] - target);                 if (dif < leastdif) {                     leastdif = dif;                     sum = nums[i] + nums[l] + nums[r];                 }                 else if (nums[i] + nums[l] + nums[r] < target) {                     l++;                 }                 else {                     r--;                 }             }         }         return sum;     } };

来自为知笔记(Wiz)