560. Subarray Sum Equals K

Medium

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

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

class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:
        counter = collections.Counter()
        counter[0] = 1 # Simple denotion that sum == k
        count = 0
        s = 0
        for num in nums:
            s += num
            count += counter[s-k]
            counter[s] += 1
        return count