from typing import List


class Solution:
    def trap(self, height: List[int]) -> int:
        res = 0
        left, right = 0, len(height) - 1
        lMax, rMax = 0, 0
        while left < right:
            lMax = max(lMax, height[left])
            rMax = max(rMax, height[right])
            if lMax < rMax:
                res += lMax - height[left]
                left += 1
            else:
                res += rMax - height[right]
                right -= 1
        return res


if __name__ == '__main__':
    print(Solution().trap([0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]))