Task

Implement the classic children's game Rock-paper-scissors, as well as a simple predictive   AI   (artificial intelligence)   player.

Rock Paper Scissors is a two player game.

Each player chooses one of rock, paper or scissors, without knowing the other player's choice.

The winner is decided by a set of rules:

   Rock beats scissors
   Scissors beat paper
   Paper beats rock


If both players choose the same thing, there is no winner for that round.

For this task, the computer will be one of the players.

The operator will select Rock, Paper or Scissors and the computer will keep a record of the choice frequency, and use that information to make a weighted random choice in an attempt to defeat its opponent.



Extra credit

Support additional choices   additional weapons.




const rps = %w(r p s)
 
const msg = [
    "Rock breaks scissors",
    "Paper covers rock",
    "Scissors cut paper",
]
 
say <<"EOT"
\n>> Rock Paper Scissors <<\n
** Enter 'r', 'p', or 's' as your play.
** Enter 'q' to exit the game.
** Running score shown as <your wins>:<my wins>
EOT
 
var plays   = 0
var aScore  = 0
var pScore  = 0
var pcf     = [0,0,0]      # pcf = player choice frequency
var aChoice = pick(0..2)   # ai choice for first play is completely random
 
loop {
    var pi = Sys.scanln("Play: ")
    pi == 'q' && break
 
    var pChoice = rps.index(pi)
 
    if (pChoice == -1) {
        STDERR.print("Invalid input!\n")
        next
    }
 
    ++pcf[pChoice]
    ++plays
 
    # show result of play
    ">> My play: %-8s".printf(rps[aChoice])
 
    given ((aChoice - pChoice + 3) % 3) {
        when (0) { say "Tie." }
        when (1) { "%-*s %s".printlnf(30, msg[aChoice], 'My point');   aScore++ }
        when (2) { "%-*s %s".printlnf(30, msg[pChoice], 'Your point'); pScore++ }
    }
 
    # show score
    "%-6s".printf("%d:%d" % (pScore, aScore))
 
    # compute ai choice for next play
    given (plays.rand.int) { |rn|
        case (rn < pcf[0])        { aChoice = 1 }
        case (pcf[0]+pcf[1] > rn) { aChoice = 2 }
        default                   { aChoice = 0 }
    }
}