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).

• 算法
  还是先排序，再左右夹逼。

• 复杂度：（0（n*n））

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;
    }
};