Problem Statement

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

Example 1:

Input: nums = [1,1,1], k = 2
Output: 2

Example 2:

Input: nums = [1,2,3], k = 3
Output: 2

Problem Link

Subarray Sum Equals K - LeetCode

Problem Visualization

Code

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int,int> m;
        
        m[0] = 1;
        int res = 0;
        int curr_sum = 0;
        for(int ele:nums)
        {
            curr_sum+=ele;
            res+=m[curr_sum-k];
            m[curr_sum]++;
        }
        return res;
    }
};

Time complexity O(n)

Space complexity O(n)