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).

同 3Sum，先排序，后两边夹逼

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int len = nums.size();
        if (len < 3) return 0;
        sort(nums.begin(), nums.end());
        int sum = 0;
        int leastdif = INT_MAX;
        for (int i = 0; i < len - 2; i++) {
            int l = i + 1, r = len - 1;
 
            while (l < r) {
                int dif = fabs(nums[i] + nums[l] + nums[r] - target);
                if (dif < leastdif) {
                    leastdif = dif;
                    sum = nums[i] + nums[l] + nums[r];
                }
                else if (nums[i] + nums[l] + nums[r] < target) {
                    l++;
                }
                else {
                    r--;
                }
            }
        }
        return sum;
    }
};

来自为知笔记(Wiz)