## 1. Problem

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 <= 10^5
- 1 <= nums[i] <= 10^9
- 1 <= k <= 10^9

## 2. Solution

I solved this problem like this.

```
class Solution:
def maxOperations(self, nums: List[int], k: int) -> int:
dic = {}
ans = 0
for x in nums:
if x not in dic:
dic[x] = 0
dic[x] += 1
for key in dic:
pair = k - key
if key == pair:
ans += dic[key] // 2
dic[key] = dic[key] % 2
continue
if k - key not in dic or pair < key:
continue
ans += min(dic[pair], dic[key])
return ans
```