Good morning! Here's our prompt for today.

The Trapping Rain Water Challenge: A Deep Dive

Imagine you're looking at an elevation map displaying rainfall over a region's landscape. The map consists of bars of varying heights, each representing different elevations. Can you determine the amount of rainwater that this uneven terrain can hold?

Problem Setup

We'll simplify the problem by using a one-dimensional array of non-negative integers. Each integer represents the height of the land at different points. The objective is to calculate the volume of rainwater that can be trapped by this series of elevations.

To better visualize this, consider the diagram below, which illustrates various elevation maps and the potential rainwater they can hold. Think of it like a game of Tetris; we aim to find how many units of rainwater could be accommodated in the available gaps.

Constraints and Performance Metrics

• Length of the array <= 100000
• Values in the array >=0
• The final answer would fit in the Integer range(< 2^32)
• Expected time complexity : O(n)
• Expected space complexity : O(1)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

function trappingRainWater(heights) {

  // Your code here

}

​

try {

  assert.equal(

    trappingRainWater([0, 0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1, 0, 0]),

    6

  );

​

  console.log(

    'PASSED: `trappingRainWater([0,0,1,0,2,1,0,1,3,2,1,2,1,0,0])` should return `6`'

  );

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(

    trappingRainWater([0, 0, 1, 0, 2, 4, 4, 4, 2, 3, 1, 0, 2, 4, 3, 1, 0, 1]),

    14

  );

​

  console.log(

    'PASSED: `trappingRainWater([0,0,1,0,2,4,4,4,2,3,1,0,2,4,3,1,0,1])` should return `14`'

  );

} catch (err) {

Here's how we would solve this problem...

How do I use this guide?