1. Count pairs with given sum.cpp

// https://bit.ly/47bCCoF

class Solution{   
public:
    int getPairsCount(int arr[], int n, int k) {
        // code here
        int ans=0;
        unordered_map<int, int> mp;
        for(int i=0;i<n;i++){
            if(mp.find(k-arr[i])!=mp.end()){
                ans+=mp[k-arr[i]];
            }
            mp[arr[i]]++;
        }
        return ans;
    }
};
};

/*
Time complexity: O(n)
Space complexity: O(n)
*/


// Code by Shumbul Arifa - https://linktr.ee/shumbul