Leetcode: 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).

比较简单，O(n^2)时间复杂度。

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