## 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 = 5Output:2Explanation: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 = 6Output:1Explanation: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}

## Rust Solution

```
struct Solution;
use std::collections::HashMap;
impl Solution {
fn max_operations(nums: Vec<i32>, k: i32) -> i32 {
let mut count: HashMap<i32, usize> = HashMap::new();
for x in nums {
*count.entry(x).or_default() += 1;
}
let mut res = 0;
for &key in count.keys() {
let a = count.get(&key).unwrap_or(&0);
let b = count.get(&(k - key)).unwrap_or(&0);
res += a.min(b);
}
(res / 2) as i32
}
}
#[test]
fn test() {
let nums = vec![1, 2, 3, 4];
let k = 5;
let res = 2;
assert_eq!(Solution::max_operations(nums, k), res);
let nums = vec![3, 1, 3, 4, 3];
let k = 6;
let res = 1;
assert_eq!(Solution::max_operations(nums, k), res);
}
```

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