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class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int res = 0;
        for (int i = 0; i < nums.size(); i ++) {
            int sum = 0;
            for (int j = i; j < nums.size(); j ++ ) {
                sum += nums[j];
                if (sum == k) {
                    res ++;
                }
            }
        }

        return res;
    }
};

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