class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int, int> mp;
        mp[0] = 1;
        int pre = 0;
        int count = 0;
        for(auto& x : nums)
        {
            pre += x;
            //判断pre-k是否在哈希表中
            if(mp.find(pre-k) != mp.end())
            {
                count += mp[pre-k];
            }
            mp[pre]++;
        }
        return count;
    }
};