Interview Question from AppBrewery - Ton Hoang Nguyen (Bill)

computeMaxArea.ts

/*
    The problem can be solve using two pointers:
        a. one (l) pointing to the first element
        b. the other one (r) pointing to the last element

    Then in a while loop, we iterate and compute the area
    by computing a distance (r - l) and taking the height
    of the building that is less tall. We then compare
    the temporary current result with the largest area
    (max).

    In a loop, we look at the area between l and r.
    We do this by finding the distance between l and r and 
    using the height of the shorter building. 
    We keep track of the biggest area we find.
    
    We keep moving l and r closer together until they meet. 
    In the end, we have found the biggest area possible
    and return it.
*/
export function maxArea(height: number[]): number {

    let l = 0, r = height.length - 1, max = 0;
    while (l < r) {
        max = Math.max(max, (r-l) * Math.min(height[l], height[r]));
        if (height[l] <= height[r]) {
            l++;
        } else {
            r--;
        }
    }
    return max;
}

computerMaxArea.test.ts

import { maxArea } from '../src/computeMaxArea'

describe('maxArea', () => {
  
  test('should return 1', () => {
    expect(maxArea([1, 1])).toBe(1);
  });

  test('should return 49', () => {
    expect(maxArea([1, 8, 6, 2, 5, 4, 8, 3, 7])).toBe(49);
  });

  test('should return 0 if there is only one building', () => {
    expect(maxArea([1, 0, 0, 0, 0])).toBe(0);
  });

  test('should return 8 if they are only two building at both ends', () => {
    expect(maxArea([5, 0, 0, 0, 2])).toBe(8);
  });

  test('should return 8 if there are only two adjacent buildings', () => {
    expect(maxArea([0, 0, 8, 8, 0, 0])).toBe(8);
  });

});

test-output.sh

(base) billtonhoang@BillTonHoangs-MacBook-Pro compute-max-area % npm run test

> [email protected] test
> node --experimental-vm-modules node_modules/.bin/jest

jest-haste-map: Watchman crawl failed. Retrying once with node crawler.
  Usually this happens when watchman isn't running. Create an empty `.watchmanconfig` file in your project's root folder or initialize a git or hg repository in your project.
  Error: Watchman error: std::__1::system_error: open: /Users/billtonhoang/Documents/GitHub/compute-max-area: Operation not permitted. Make sure watchman is running for this project. See https://facebook.github.io/watchman/docs/troubleshooting.
(node:51889) ExperimentalWarning: VM Modules is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
 PASS  __test__/computeMaxArea.test.ts
  maxArea
    ✓ should return 1 (2 ms)
    ✓ should return 49 (1 ms)
    ✓ should return 0 if there is only one building
    ✓ should return 8 if they are only two building at both ends
    ✓ should return 8 if there are only two adjacent buildings

Test Suites: 1 passed, 1 total
Tests:       5 passed, 5 total
Snapshots:   0 total
Time:        1.365 s, estimated 2 s
Ran all test suites.