[leetcode] 560. Subarray Sum Equals K

Description

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

Example 1:
Input:

nums = [1,1,1], k = 2

Output:

2

Note:

1. The length of the array is in range [1, 20,000].
2. The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].

分析

题目的意思是：找出一个数组里面连续子数组的和为K的子数组的个数。

• 用一个map存起来，mp[0]的初始值为1，用于然后mp记录的是前m项的求和，mp[sum-k]如果为1，表明存在一个连续子序列的值为k，这需要找个test case模拟一下就行了。

代码

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

参考文献

​​LeetCode Subarray Sum Equals K 子数组和为K​​​​560. Subarray Sum Equals K​​