HardArraysFree practice
Trapping Rain Water
Asked atgoogleamazonmetamicrosoftgoldman-sachsapplebloomberg
01 · 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.
02 · Examples
Example 01
Input
height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output
6
Water fills the valleys between bars. The total trapped water is 6 units.
Example 02
Input
height = [4,2,0,3,2,5]
Output
9
Water fills the gaps between the tall bars on each side, trapping 9 units total.
Example 03
Input
height = [1,0,1]
Output
1
One unit of water is trapped between the two bars of height 1.
03 · Constraints
- 01n == height.length
- 021 <= n <= 2 * 104
- 030 <= height[i] <= 105
04 · Optimal complexity
- Time
- O(n)
- Space
- O(1)
05 · Two ways to work on it
Practice it alone or rehearse it as an interview.
Practice Mode gives you an editor and test runs, nothing else. AI Interview Mode puts a voice interviewer on the other side, adds a clock, and ends with a scored summary of the round.