LeetCode75——Day13

一、题目

1679. Max Number of K-Sum Pairs

You are given an integer array nums and an integer k.

In one operation, you can pick two numbers from the array whose sum equals k and remove them from the array.

Return the maximum number of operations you can perform on the array.

Example 1:

Input: nums = [1,2,3,4], k = 5
Output: 2
Explanation: Starting with nums = [1,2,3,4]:

• Remove numbers 1 and 4, then nums = [2,3]
• Remove numbers 2 and 3, then nums = []
  There are no more pairs that sum up to 5, hence a total of 2 operations.
  Example 2:

Input: nums = [3,1,3,4,3], k = 6
Output: 1
Explanation: Starting with nums = [3,1,3,4,3]:

• Remove the first two 3’s, then nums = [1,4,3]
  There are no more pairs that sum up to 6, hence a total of 1 operation.

Constraints:

1 <= nums.length <= 105
1 <= nums[i] <= 109
1 <= k <= 109

二、题解

排序+双指针

class Solution {
public:
    int maxOperations(vector<int>& nums, int k) {
        int n = nums.size();
        sort(nums.begin(),nums.end());
        int i = 0,j = n - 1,res = 0;
        while(i < j){
            if(nums[i] + nums[j] == k){
                res++;
                i++;
                j--;
            }
            else if(nums[i] + nums[j] > k) j--;
            else if(nums[i] + nums[j] < k) i++;
        }
        return res;
    }
};