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560. Subarray Sum Equals K

Difficulty Topics

Description

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

subarray-sum-equals-k.py
class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:
        mp = defaultdict(int)
        mp[0] = 1

        s = res = 0

        for x in nums:
            s += x

            if s - k in mp:
                res += mp[s - k]

            mp[s] += 1

        return res