leetcode_c++：3Sum Closest(016)

题目

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).

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• 算法
  还是先排序，再左右夹逼。

• 复杂度：（0（n*n））

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class Solution {public:    int threeSumClosest(vector<int> &num, int target) {        int ret = num[0] + num[1] + num[2];        int len = num.size();        sort(num.begin(), num.end());        for (int i = 0; i <= len - 3; i++) {            // first number : num[i]            int j = i + 1;    // second number            int k = len - 1;    // third number            while (j < k) {                int sum = num[i] + num[j] + num[k];                if (abs(sum - target) < abs(ret - target))                    ret = sum;                if (sum < target) {                    ++j;                } else if (sum > target) {                    --k;                } else {                    ++j;                    --k;                }            }        }        return ret;    }};