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;
    }
};

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