← Blog

JavaScript Katas: Draw Chessboard

August, 2020

Intro 🌐

Problem solving is an important skill, for your career and your life in general.

That’s why I take interesting katas of all levels, customize them and explain how to solve them.


Understanding the Exercise❗

First, we need to understand the exercise! If you don’t understand it, you can’t solve it!.

My personal method:

  1. Input: What do I put in?
  2. Output: What do I want to get out?

Today’s exercise

Today, another 7 kyu kata, meaning we slightly increase the difficulty.

Source: Codewars

Write a function drawChessboard, that accepts two parameters: rows and columns.

Given a rows number, e.g. 3, and a columns number, e.g. 3, return a chessboard as a two dimensional array, e.g.

[
  [ "O", "X", "O" ],
  [ "X", "O", "X" ],
  [ "O", "X", "O" ]
]

White should be represented by "O", black by "X", the first row starts with a "O".


Input: two numbers.

Output: an array of array(s).


Thinking about the Solution 💭

I think I understand the exercise (= what I put into the function and what I want to get out of it).

Now, I need the specific steps to get from input to output.

I try to do this in small baby steps:

  1. Create a row with the correct length (= columns) that starts with "O"
  2. Create a row with the correct length (= columns) that starts with "X"
  3. Do this alternately until there are enough (= rows) rows
  4. Return the array of array(s)

Example:

  • Input: 3, 3
  • Create a row with the correct length (= columns) that starts with "O": [ "O", "X", "O" ]
  • Create a row with the correct length (= columns) that starts with "X": [ "X", "O", "X" ]
  • Do this alternately until there are enough (= rows) rows: 1 additional row (=> 3 - 2 = 1) : [ "O", "X", "O" ]
  • Return the array of array(s): [ [ "O", "X", "O" ], [ "X", "O", "X" ], [ "O", "X", "O" ]]
  • Output: [ [ "O", "X", "O" ], [ "X", "O", "X" ], [ "O", "X", "O" ]]

Implementation (Explicit) ⛑

function drawChessboard(rows, columns) {
  // Create an empty board with the correct amount of rows
  const board = [...Array(rows)].map((_) => []);

  // Create a row with the correct length that starts with "O"
  const rowO = [...Array(columns)].map((_, i) => (i % 2 ? "X" : "O"));

  // Create a row with the correct length that starts with "X"
  const rowX = [...Array(columns)].map((_, i) => (i % 2 ? "O" : "X"));

  // Add the proper row to each board row
  return board.map((_, i) => (i % 2 ? rowX : rowO));
}

Result

console.log(drawChessboard(3, 3));
/*
[
  [ "O", "X", "O" ],
  [ "X", "O", "X" ],
  [ "O", "X", "O" ]
]
*/
// ✅

console.log(drawChessboard(2, 4));
/*
[
  [ "O", "X", "O", "X" ],
  [ "X", "O", "X", "O" ]
]
*/
//  ✅

Implementation (Implicit) ⛑

function drawChessboard(rows, columns) {
  return [...Array(rows)]
    .map((_) => [])
    .map((_, i) =>
      i % 2
        ? [...Array(columns)].map((_, i) => (i % 2 ? "O" : "X"))
        : [...Array(columns)].map((_, i) => (i % 2 ? "X" : "O"))
    );
}

Result

console.log(drawChessboard(3, 3));
/*
[
  [ "O", "X", "O" ],
  [ "X", "O", "X" ],
  [ "O", "X", "O" ]
]
*/
// ✅

console.log(drawChessboard(2, 4));
/*
[
  [ "O", "X", "O", "X" ],
  [ "X", "O", "X", "O" ]
]
*/
//  ✅

Playground ⚽

You can play around with the code here


Next Part ➡️

Great work!

We learned how to use ..., Array, map.

I hope you can use your new learnings to solve problems more easily!

Next time, we’ll solve another interesting kata. Stay tuned!


If I should solve a specific kata, shoot me a message here.

If you want to read my latest stuff, get in touch with me!


Further Reading 📖


Questions ❔

  • How often do you do katas?
  • Which implementation do you like more? Why?
  • Any alternative solution?

miku86

Hi! I'm Michael 👋 I'm a Mentor & Educator & Senior Web Developer - I help you to reach your (career) goals.