Formatted question description: https://leetcode.ca/all/560.html

# 560. Subarray Sum Equals K

Medium

## 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].

## Solution

Use a map to store each sum and the count of subarrays of the sum. Put sum 0 with count 1 to the map initially.

Loop over nums and calculate the total sum sum. For each num in nums, add num to sum, and obtain the count of subarrays with sum sum - k. Add the sum to the result. Then update the map with the count of subarrays with sum sum. Finally, return the result.

Java

class Solution {
public int subarraySum(int[] nums, int k) {
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(0, 1);
int count = 0;
int sum = 0;
int length = nums.length;
for (int i = 0; i < length; i++) {
sum += nums[i];
int curCount = map.getOrDefault(sum - k, 0);
count += curCount;
int sumCount = map.getOrDefault(sum, 0);
map.put(sum, sumCount + 1);
}
return count;
}
}