Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Example 1:
Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.
Example 2:
Input: height = [4,2,0,3,2,5]
Output: 9
Solution
class Solution:
def trap(self, height: List[int]) -> int:
left = 0
right = len(height) - 1
water = 0
max_left = height[left]
max_right = height[right]
while left < right:
if height[left] <= height[right]:
left += 1
max_left = max(max_left, height[left])
water += max_left - height[left]
else:
right -= 1
max_right = max(max_right, height[right])
water += max_right - height[right]
return water