16. 3Sum Closest

[fockspaces]

Given an integer array nums of length n and an integer target, find three integers in nums such that the sum is closest to target.

Return the sum of the three integers.

You may assume that each input would have exactly one solution.

Example 1:

Input: nums = [-1,2,1,-4], target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2:

Input: nums = [0,0,0], target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0).

Constraints:

3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104

[fockspaces]

跟 3 sum 差不多思路，先排序後再用雙指針限縮範圍 如果直接找到 target 則 return

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