trapping rainwater

Problem: Trapping rain water.

code:

class Solution:
    def trap(self, height: List[int]) -> int:
        l , r = 0,len(height) - 1
        maxl , maxr = 0,0
        water = 0
        maxwater =0 
        while l <r:
            if height[l] <= height[r]:
                if height[l] >= maxl:
                    maxl =  height[l]
                else:
                    water+=maxl - height[l]
                l+=1
            else:
                if height[r] >=maxr:
                    maxr = height[r]
                else:
                    water +=maxr-height[r]
                r-=1
        return water

time complexity: O(n)

space complexity: O(1)