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Max Number of K-Sum Pairs

Updated: Jan 18, 2021

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

Solution:

class Solution {
    public int maxOperations(int[] nums, int k) {
        int left,right,count=0;
        Arrays.sort(nums);
        left=0;
        right=nums.length-1;
        while(left<right)
        {
            if(nums[left]+nums[right]==k)
            {
                count++;
                left++;
                right--;
            }
            else if(nums[left]+nums[right]>k)
            {
                right--;
            }
            else
            {
                left++;
            }
        }
        return count;
    }
}




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