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:

1 2 3 4

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.

sum = 0 left = 0 right = height.__len__() - 1 leftMax = 0 rightMax = 0

while left < right: if height[left] < height[right]: if height[left] > leftMax: leftMax = height[left] else: sum += leftMax - height[left] left += 1 else: if height[right] > rightMax: rightMax = height[right] else: sum += rightMax - height[right] right -= 1