Mastermind is a simple two-player logical puzzle game. In it, one player sets a “code”, comprised of pins of different colours, and the other tries to break the code by guessing, and receives “feedback”, i.e., how many pins he/she got right in a certain way. The player then constructs his/her subsequent guesses based on his/her inferences from the feedback. The goal of the game is to guess the code correctly before chances run out.

You can find more about mastermind here.

Representing Pins as Unicode Characters

The first issue we need to address when trying to code a game of mastermind is printing the pins. The output is, by default, a dull off-white colour (I use IntelliJ’s dark theme). So, we need 6 different colours, one for each pin. The colours we shall use are red, green, blue, magenta, cyan and yellow. The unicode values for these can be found here. Note that you will need to use the reset unicode after each time you print with non-default colours. Now, the symbol for the pin. We can use the “large filled circle” symbol (unicode: \u2B24), and assign it a colour. The colours can be stored in a map/dictionary. For the feedback pins, we can use the bullet symbol (unicode: \u2022), which needs to be either red or white in colour.

The Logic Behind Mastermind

Flowchart depicting the sequence of events in a game of mastermind.

In a game of mastermind, the code-setter, in this case the computer, sets a random 4-pin long code. Then, the computer prompts the user to input his/her guess. The computer then reads the guess, decrements the chances, and prints the user’s guesses so far along with their feedback. This is looped until the code is guessed or the chances have been exhausted.

Putting it Together in Scala

First, we need to create classes for a Pin and a Code. The Pin class takes in a letter (r, g, b, y, m or c) as its only parameter and upon initialisation, creates a symbol in unicode characters for itself.

// class Pin
class Pin(_name: String) {
  val colors: Map[String, String] = Map("R" -> "\u001B[31m", "G" -> "\u001B[32m", "B" -> "\u001B[34m",
    "Y" -> "\u001B[33m", "C" -> "\u001B[36m", "M" -> "\u001B[35m")
  val name: String = _name
  val color = f"${colors(name)}\u2B24${"\u001B[0m"}"

The Code class takes 4 pins as parameters. It has a function to print the code. Additionally, it has a function to check if it is the same as another code fed to it, and then provides feedback for the code.

// class Code
class Code(p1: Pin, p2: Pin, p3: Pin, p4: Pin) {
  val code: Array[Pin] = Array(p1, p2, p3, p4)
  var correctcolor = 0
  var correctpos = 0
  var guessed = false

  def print_code(): Unit = {
    for (pin <- code) {
      if (code.indexOf(pin) == 0) {
        printf(f"| ${pin.color} |")
      else if (code.indexOf(pin)== 3) {
        printf(f" ${pin.color} |")
        for (_ <- 0 until correctcolor){
        for (_ <- 0 until correctpos){
        printf(f" ${pin.color} |")

  def check(original: Code): Unit={
    var used : ArrayBuffer[String]= ArrayBuffer()
    for (pin <- code){
      for (orpin <- original.code){
        if ( == && used.indexOf( == -1){
          if (code.indexOf(pin)==original.code.indexOf(orpin)){
            correctpos += 1
          else {
            correctcolor += 1
          used = used :+
    if (correctpos == 4){
      original.guessed = true


Now for the main object. We define a function to choose a random code. Since we do not want to repeat a colour, we pop the random colour chosen from the list of colours. We then define a function to take in a valid user input. The play() function calls the user input function in a while loop under the main() function. The while loop runs until the word is guessed or the chances are over. The game ends after the termination of the while loop. You could also create a function to print instructions at the beginning.

object mastermind {
  val colorlist: Array[String] = Array("R", "G", "B", "Y", "M", "C")
  val original: Code = random_code()
  var codes: ArrayBuffer[Code] = ArrayBuffer()

  def main(args: Array[String]): Unit = {
    var chances = 10
    while(chances > 0 && !original.guessed){
      for (code <- codes){
        if (codes.indexOf(code) == codes.length-1){
      chances -= 1
    if (chances == 0 && !original.guessed){
      println("Oh no, you lost! The code was:")
      println("Congratulations, you guessed the code!")

  def play(): Unit ={
    val guess = user_input()
    val guesscode = new Code(new Pin(guess(0)), new Pin(guess(1)), new Pin(guess(2)), new Pin(guess(3)))
    codes = codes :+ guesscode

  def random_code(): Code ={
    var tempclist: ArrayBuffer[String] = ArrayBuffer()
    var codeparams: ArrayBuffer[Pin]= ArrayBuffer()
    for (i <- colorlist){
      tempclist = tempclist :+ i
    for (_ <- 0 until 4){
      val rand_index = Random.nextInt(tempclist.length)
      val pin = new Pin(tempclist(rand_index))
      tempclist -= tempclist(rand_index)
      codeparams = codeparams :+ pin
    val code = new Code(codeparams(0), codeparams(1), codeparams(2), codeparams(3))
    return code

  def user_input(): Array[String] ={
    var valid = 4
    var input ="Enter your guess: ").split(" ").map(_.toUpperCase)
    for (i <- input){
      if (colorlist.indexOf(i) == -1){
        valid -= 1
    if (valid != 4){
      input = user_input()
    return input

  def print_instructions(): Unit ={
    println("1. Your goal is to break the code. You have 10 chances. The code has no repeated pins.")
    println("2. There are 6 colours - red(R/r), green(G/g), blue(B/b), yellow(Y/y), cyan(C/c), magenta(M/m).")
    println("3. Input your answer as 4 space separated characters. eg. r r g y")
    println("4. The feedback is given in the form of red and white bullets.")
    println("5. Red signifies that a pin is in its correct position.")
    println("6. White signifies that a pin is in the code but not in its correct position.")
    println("7. Since the pins are checked one by one, if a pin of a certain color is repeated in the input, the feedback of only the first occurrence of that pin is counted.")
    println("8. That's all for now. Good Luck!")
    println(s"${"\u001B[1m"}GAME STARTS${"\u001B[0m"}")


Coming soon: Coding an AI agent to play mastermind using a Genetic Algorithm

You can try playing around with the length of the code and the number of colours. Also, you could make an AI program to win a game of mastermind, by working with a logical knowledge base.

The github link for the above program is:

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