Leetcode:523. Continuous Subarray Sum

c++code:

class Solution {  
public:  
    bool checkSubarraySum(vector<int>& nums, int k) {  
        unordered_map<int, int> hash;  
        int sum = 0;  

        hash[0] = -1;  
        for(int i=0; i<nums.size(); ++i) {  
            sum += nums[i];  
            if(k) sum %= k;  
            if(hash.find(sum) != hash.end()) {  
                if(i-hash[sum] > 1) return true;  
            }  
            else hash[sum] = i;  
        }  

        return false;  
    }  
};