Subarray sum equals k (only positive integers)

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

        left = 0
        right = 0
        window_sum = 0
        count = 0

        while right < len(nums):

            # add the right to the window
            window_sum += nums[right]

            # shrink the window untill we have sum < k
            while window_sum > k:
                window_sum -= nums[left]
                left += 1

            # if current window has sum equal to k
            if window_sum == k:
                count += 1

            # expand the window
            right += 1

        return count