LeetCode题解：3sum closest

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).

思路：

类似3Sum，只不过每次求和的时候都和已知的最接近的值比对一下，随时更新已经找到的最优解。

题解：

class Solution {public:    int threeSumClosest(vector<int> &num, int target) {        int closest = numeric_limits<int>::max();        int sum = 0;                sort(begin(num), end(num));                for(size_t i = 0; i < num.size() - 2; ++i)        {            int j = i + 1;            int k = num.size() - 1;            int expectation = target - num[i];                        while(j < k)            {                int diff = expectation - num[j] - num[k];                if (abs(closest) > abs(diff))                {                    closest = diff;                    sum = target - diff;                }                                if (diff < 0)                    k--;                else if (diff > 0)                    j++;                else                    return target;            }        }                return sum;    }};