leetcode

0 class Solution {

1 public:

2 int subarraySum(vector<int> &nums, int k) {

3 int n = nums.size(), res = 0, sum = 0;

4 unordered_map<int, int> um;

5 vector<int> prefix(n);

6 for (int i = 0; i < n; i++)

7 sum = prefix[i] = sum + nums[i];

8

9 for (int i = 0; i < n; i++) {

10 if (prefix[i] == k) res++;

11 if (um.count(prefix[i] - k)) res += um[prefix[i] - k];

12 um[prefix[i]]++;

13 }

14

15 return res;

16 }

17 };