GFG PTOD | 27 Dec | Count pairs with given sum

int countPairs(vector<int> &arr, int target) {
        // Code here
        map<int, int> mp;
        int count = 0;
        for(int i=0; i<arr.size(); i++) {
            if(mp.count(arr[i])){
                count += mp.find(arr[i])->second;
            }
            mp[target - arr[i]]++;
        }
        return count;
    }