LeetCode 42 - Trapping Rain Water - 2022.12.30 solution - two pointers

class Solution:
    def trap(self, height: List[int]) -> int:
        """ How to solve it: We're going to try to implement the O(1) memory two-pointer
        solution.  So we don't need a result array, we just need an integer tracking the
        amount of trapped water.  We're then going to step inwards from the left and
        right, and whichever side has the smaller max height from that side, that will
        be the side we will add to the water, and then step inwards from that side.
        """
        l = 0
        r = len(height) - 1
        water = 0
        max_l_height = 0
        max_r_height = 0

        while l <= r:
            if max_l_height <= max_r_height:
                water += max(0, max_l_height - height[l])
                max_l_height = max(max_l_height, height[l])
                l += 1
            else:
                water += max(0, max_r_height - height[r])
                max_r_height = max(max_r_height, height[r])
                r -= 1
        return water