water_area.py

water_arr = [4, 2, 0, 3, 2, 5]

def water_area(water_arr):
	left_max = []
	right_max = []
	wa_idx_left = 0
	wa_idx_right = len(water_arr)

	while wa_idx_left < len(water_arr) and wa_idx_right >= 0:
		highest_left = max(water_arr[:wa_idx_left]) if water_arr[:wa_idx_left] else 0
		left_max.append(highest_left)
		highest_right = max(water_arr[wa_idx_right:]) if water_arr[wa_idx_right:] else 0
		right_max.append(highest_right)
		wa_idx_left +=1
		wa_idx_right -=1

	right_max = right_max[::-1]
	total_area = 0
	for left, right, idx in zip(left_max, right_max, water_arr):
		smallest_pillar = min(left, right)
		if left > idx < right:
			total_area += abs(smallest_pillar-idx)
	return total_area