LeetCode 560. Sum array of K (prefix and difference)

1. Title

Given an array of integers and an integer k, you need to find the number of consecutive subarrays in the array whose sum is k .

示例 1 :
输入:nums = [1,1,1], k = 2
输出: 2 , [1,1] 与 [1,1] 为两种不同的情况。
说明 :
数组的长度为 [1, 20,000]。
数组中元素的范围是 [-1000, 1000] ，且整数 k 的范围是 [-1e7, 1e7]。

Source: LeetCode (LeetCode)
link: https://leetcode-cn.com/problems/subarray-sum-equals-k The
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2. Problem solving

Similar topics: LeetCode 1248. Statistics "beautiful sub-array" (to be reviewed)

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int, int> m;//和，数组个数
        int i, sum = 0, count = 0;
        m[0] = 1;//边界，和为0的子数组数量为1
        for(i = 0; i < nums.size(); ++i)
        {
        	sum += nums[i];
        	// m[sum]++;不能写在这
        	count += m[sum-k];
            m[sum]++;
        }
        return count;
    }
};

96 ms 21.2 MB