1def trap(height):2    l = 03    r = len(height) - 14    max_water = 05    max_l = height[l]6    max_r = height[r]7    while l < r:8        if max_l < max_r:9            l += 110            max_l = max(max_l, height[l])11            max_water += max_l - height[l]12        else:13            r -= 114            max_r = max(max_r, height[r])15            max_water += max_r - height[r]16    return max_water