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miku86
miku86

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JavaScript Katas: Draw Chessboard

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" ]
]
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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 πŸ’­

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" ]] βœ…

Implementation (Explicit) β›‘

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));
}
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Result

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

console.log(drawChessboard(2, 4));
/*
[
  [ "O", "X", "O", "X" ],
  [ "X", "O", "X", "O" ]
]
*/
//  βœ…
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Implementation (Implicit) β›‘

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"))
    );
}
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Result

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

console.log(drawChessboard(2, 4));
/*
[
  [ "O", "X", "O", "X" ],
  [ "X", "O", "X", "O" ]
]
*/
//  βœ…
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Playground ⚽

You can play around with the code here


Next Part ➑️

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 πŸ“–


Questions ❔

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

Discussion (5)

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kosich profile image
Kostia Palchyk

πŸ‘

I think, your second solution can even be a bit shortened:

function drawChessboard(rows, columns) {
  return [...Array(rows)]
    .map((_, i) =>
      [...Array(columns)].map((_, j) => ((j+i) % 2 ? "X" : "O"))
    );
}
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gerges27 profile image
Gerges Nady

let arr = new Array()
let j = 0
let defArr = []
while (j <= m) {
defArr.push("o")
defArr.push("x")
j++
}
let x = defArr.slice(0, m)
let y = defArr.reverse().slice(0, m)

let count = 1
for (let i = 0; i < n; i += 2) {
    arr[i] = x
    if (count < n) {
        arr[count] = y
        count += 2
    }
}
console.log(arr)
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miku86 profile image
miku86 Author

Hey Gerges,

great work solving all these katas.
Looking forward to seeing some other solutions!

Collapse
gerges27 profile image
Gerges Nady

Ok, thanks

Collapse
kosich profile image
Kostia Palchyk • Edited on

Couldn't let this kata go out of my mind, wanted to try something alternative:

const drawChessboard = (r, c) => [
    ...{ * [Symbol.iterator]() {
      for (let i = 0; i < r; i++) yield [
        ...{ * [Symbol.iterator]() {
          for (let j = i; j < c + i; j++) yield ['X', 'O'][j % 2]
        }}
      ]
    }}
  ]