Trapping Rain Water
Updated Jan 31, 2026
Problem
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.
Constraints
n == height.length
1 <= n <= 2 * 10^4
0 <= height[i] <= 10^5
Examples
Example 1
Input:
height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output:
6
6 units of rain water are trapped.
Example 2
Input:
height = [4,2,0,3,2,5]
Output:
9
Function Signature
def trap(self, height: list[int]) -> int
How to Submit
Implement a Solution class with a trap method.
Your method will be called with the input parameters and should return the answer.