LeetCode.560 Subarray Sum Equals K

1.Problem
https://leetcode.com/problems/subarray-sum-equals-k/

2.Idea
Using map for every sum of {0..i} and count.

3.Source

 class Solution {  
 public:  
      map<int, int> mp;  
      int sum = 0;  
      int subarraySum(vector<int>& nums, int k) {      
           int ans = 0;  
     mp[0] = 0;  
           for (int i = 0; i < nums.size(); i++) {  
                sum += nums[i];  
                if(sum == k) ans++;  
       mp[sum]++;  
                if (mp.find(sum - k) != mp.end()) {  
                     ans += mp[sum - k];  
                }  
           }  
     if(k == 0) return ans - nums.size();  
           else return ans;  
      }  
 };