Subarray Sum Equals K

Problem Statement

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.

Leetcode Link

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

Code

Python Code

class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:

        ans=0
        prefsum=0
        d={0:1}

        for num in nums:
            prefsum = prefsum + num

            if prefsum-k in d:
                ans = ans + d[prefsum-k]

            if prefsum not in d:
                d[prefsum] = 1
            else:
                d[prefsum] = d[prefsum]+1

        return ans