# 1679. Max Number of K-Sum Pairs

Max Number of K-Sum Pairs - LeetCode

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
``````

• code
``````class Solution:
def maxOperations(self, nums: List[int], k: int) -> int:
need_map = defaultdict(int)
res = 0
for v in nums:
if need_map[v] == 0:
need_map[k - v] += 1
else:
need_map[v] -= 1
res += 1
return res
``````