Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 4

Description

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

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
  unordered_map<int, int> count;
public:
  int maxOperations(vector<int>& nums, int k) {
    for(auto i : nums) count[i] += 1;
    int answer = 0;
    for(auto [num, cnt] : count) {
      if(!count.count(k-num)) continue;
      answer += min(cnt, count[k-num]);
    }
    answer /= 2;
    return answer;
  }
};

// Accepted
// 51/51 cases passed (149 ms)
// Your runtime beats 82.22 % of cpp submissions
// Your memory usage beats 31.86 % of cpp submissions (68.4 MB)