[LeetCode]16. 3Sum Closest

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).

分析

k-Sum系列问题的扩展，解题思路还是先排序，然后选定一个数后，在这个选定数后续序列里通过两端夹逼的方式遍历剩下的两个数的组合，遍历过程中记录最接近target的和即可

源码

class Solution {public:    // 排序 两边夹逼    int threeSumClosest(vector<int>& nums, int target) {        int ret;        int gap = INT_MAX;        sort(nums.begin(), nums.end());        for(int i = 0; i < nums.size() - 2; i++) {            int j = i + 1;            int k = nums.size() - 1;            while(j < k) {                int sum = nums[i] + nums[j] + nums[k];                int tmp_gap = abs(sum - target);                if(tmp_gap < gap) {                    ret = sum;                    gap = tmp_gap;                }                if(sum > target) k--;                else j++;            }        }        return ret;    }};