Subarrays with given sum

Given an unsorted array arr[] of N integers and a sum. The task is to count the number of subarrays which add to a given number.

• Time : O(n)
• Space : O(n)

class Solution {
public:
    int subArraySum(int arr[], int n, int sum) {
        unordered_map<int, int> mp{{0,1}};
        int res = 0;
        for(int i = 0, s = 0; i < n; i++) {
            s += arr[i];
            int target = s - sum;
            res += mp[target];
            mp[s]++;
        }
        
        return res;
    }
};