560. Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.

c++

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int, int> m;
        m[0]++;
        int sum = 0, res = 0;
        for(auto& num : nums) {
            sum += num;
            res += m[sum - k];
            m[sum]++;
        }

        return res;
    }
};