"""
1679. Max Number of K-Sum Pairs
Medium

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

"""
class Solution:
    def maxOperations(self, nums: List[int], k: int) -> int:
        count = Counter(nums)
        nums = sorted(count.keys(), reverse=True)
        ops = 0
        i = nums.pop()
        while i < (k//2)+1:
            if k %2 == 0 and i == k/2:
                ops += count[i]//2
            else:
                ops += min(count[i], count[k-i])
            if not nums:
                break
            i = nums.pop()
        return ops

