Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Example 1:

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

 

Note:

1. The length of the array is in range [1, 20,000].
2. The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].

 

class Solution {public:    int subarraySum(vector
       
        & nums, int k) {        int n=nums.size();        if (n==0)            return 0;               vector
        
          sum(n+1,0);        for (int i=1; i<=n; i++)            sum[i]=nums[i-1]+sum[i-1];                unordered_map
         
           hash;        hash[0]=1;        int res=0;        for (int i=1; i<=n; i++)        {            if (hash[sum[i]-k])                res+=hash[sum[i]-k];            hash[sum[i]]++;        }        return res;    }};