// Code help from Apna College ..

class Solution {
public:
    int subarraySum(vector<int>& arr, int k) {
        int n = arr.size();
        int count = 0;
        vector<int> prefixSum(n,0);

        prefixSum[0] = arr[0];
        for(int i=1 ; i<n ; i++){
            prefixSum[i] = prefixSum[i-1] + arr[i];
        }

        unordered_map<int, int> m;
        for(int j=0 ; j<n ; j++){
            if(prefixSum[j] == k) count++;

            int val = prefixSum[j] - k;
            if(m.find(val) != m.end()){
                count +=m[val];

            }

            if(m.find(prefixSum[j]) == m.end()){
                m[prefixSum[j]] = 0;

            }
            m[prefixSum[j]]++;

        }
        return count ;

    }
};


