560. Subarray Sum Equals K

560. Subarray Sum Equals K

和https://leetcode.com/problems/path-sum-iii/思路相同

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int, int> map;
        map[0] = 1;
        int count = 0;
        int curSum = 0;
        for(auto& num : nums)
        {
            curSum += num;
            if(map.find(curSum - k) != map.end())
                count += map[curSum - k];
            map[curSum] += 1; // 之所以要后面加，是为了当k=0时候，如果前面加意味着当前位都不去，那不行啊
        }
        return count;
    }
};