leetcode 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).

解：这一题需要先进行排序，这样就可以将三方的复杂度降低到平方的复杂度。假定一个id1后遍历后面的数组，然后后移id1.

class Solution {public:    int threeSumClosest(vector<int>& nums, int target) {        if(nums.size() < 3) return 0;        int closest = nums[0]+nums[1]+nums[2];        std::sort(nums.begin(), nums.end());        for(int first = 0 ; first < nums.size()-2 ; ++first) {            if(first > 0 && nums[first] == nums[first-1]) continue;            int second = first+1;            int third = nums.size()-1;                        while(second < third) {                int curSum = nums[first]+nums[second]+nums[third];                if(curSum == target) return curSum;                if(abs(target-curSum)<abs(target-closest)) {                    closest = curSum;                }                if(curSum > target) {                    --third;                } else {                    ++second;                }            }        }        return closest;    }};