Sword finger offer II 010 Subarray prefix sum difference with sum K

The finger of the sword Offer II 010. And for k Subarray

class Solution {
    
public:
    int subarraySum(vector<int>& nums, int k) {
    
		unordered_map<int,int> mapp;
		mapp[0]=1;
		int pre=0,resCnt=0;
		for(auto& x:nums){
    
			pre+=x;
			if(mapp.find(pre-k)!=mapp.end()){
    
				resCnt+=mapp[pre-k];
			}
			mapp[pre]++;
		}
		return resCnt;
    }
};