def rain_water(heights):
    # Initialize two pointers at the leftmost and rightmost positions of the elevation map
	left = 0
	right = len(heights) - 1

    # Variables to store the accumulated rainwater and maximum heights
	stored_water = 0
	left_max, right_max = 0, 0
	
	while left <= right:

		# If the maximum height on the right is less than or equal to the maximum height on the left
		if  left_max > right_max:
			stored_water +=  max(0, right_max - heights[right])

			# Update the right maximum height if necessary
			right_max = max(right_max, heights[right])
			right -= 1
        
		# If the maximum height on the left is less than the maximum height on the right
		else:
			stored_water += max(0, left_max - heights[left])

			# Update the left maximum height if necessary
			left_max = max(left_max, heights[left])
			left +=1

	return stored_water

# Driver code
def main():
    input_list = [
                [1, 0, 1, 2, 1, 4, 0, 3, 5], 
                [2, 0, 9, 6],
                [3, 1, 2, 0, 2],
                [4, 2, 5, 3], [3, 0]
				
                ]
    index = 1
    for i in input_list:
        print(str(index)+".\tHeights: "+str(i))
        print("\tMaximum rainwater: " + str(rain_water(i)))
        index += 1
        print("-" * 100)


if __name__ == "__main__":
    main()