LeetCode - Trapping Rain Water

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

 

Constraints:

• n == height.length
• 1 <= n <= 2 * 104
• 0 <= height[i] <= 105

 

ChatGPT's Solution:

class Solution(object):
    def trap(self, height):
        """
        :type height: List[int]
        :rtype: int
        """

        if not height or len(height) < 3:
            return 0
        
        left, right = 0, len(height) - 1
        left_max, right_max = height[left], height[right]
        water = 0

        while left < right:
            if left_max < right_max:
                left += 1
                left_max = max(left_max, height[left])
                water += max(0, left_max - height[left])
            else:
                right -= 1
                right_max = max(right_max, height[right])
                water += max(0, right_max - height[right])
        
        return water