560. Subarray Sum Equals K | LeetCode Solution

 560. Subarray Sum Equals K | LeetCode Solution

Given an array of integers nums and an integer k, return the total number of 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

 

Constraints:

• 1 <= nums.length <= 2 * 104
• -1000 <= nums[i] <= 1000
• -107 <= k <= 107

class Solution {

public:

    int subarraySum(vector<int>& nums, int k) {

        unordered_map<int,int>mymap;

        

        int sum=0,ans=0;

        mymap[sum]=1;

        for(int i=0; i<nums.size(); i++){

            sum+=nums[i];

            auto it=mymap.find(sum-k);

            if(it!=mymap.end())ans+=mymap[sum-k];

            mymap[sum]++;

        }

        return ans;

    }

};