Count_pairs_with_given_sum.cpp

#include <bits/stdc++.h>
using namespace std;



class Solution{   
public:
    int getPairsCount(int arr[], int n, int k) {
        
         unordered_map<int, int> freqMap;
        int pairsCount = 0;
        
        for (int i = 0; i < n; i++) {
            int complement = k - arr[i];
            pairsCount += freqMap[complement];
            freqMap[arr[i]]++;
        }
        
        return pairsCount;
    }
};


int main() {
    int t;
    cin >> t;
    while (t--) {
        int n, k;
        cin >> n >> k;
        int arr[n];
        for (int i = 0; i < n; i++) {
            cin >> arr[i];
        }
        Solution ob;
        auto ans = ob.getPairsCount(arr, n, k);
        cout << ans << "\n";
    }
    
    return 0;
}