Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.

A subarray is a contiguous non-empty sequence of elements within an array.

Example 1:

Input: nums = [1,1,1], k = 2
Output: 2

Example 2:

Input: nums = [1,2,3], k = 3
Output: 2

Constraints:

• 1 <= nums.length <= 2 * 104
• -1000 <= nums[i] <= 1000
• -107 <= k <= 107

SOLUTION:

class Solution: def subarraySum(self, nums: List[int], k: int) -> int: n = len(nums) curr = 0 prevsum = {} ctr = 0 for num in nums: curr += num if curr == k: ctr += 1 if (curr - k) in prevsum: ctr += prevsum[curr - k] prevsum[curr] = prevsum.get(curr, 0) + 1 return ctr