[leetcode]560. Subarray Sum Equals K

[leetcode]560. Subarray Sum Equals K

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Analysis

ummm 心情复杂—— [每天刷题并不难0.0]

Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Explanation:

计算pre sum，再结合hashmap就可以了

Implement

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