ttt.R

# TIC TAC TOE
# Run function ttt(n) to begin

ttt <- function (n = 3) {
  
  # set up board variables
  board <- matrix(rep(".", (n+1)^2), ncol=n+1)
  board[,1] <- c("/", 1:n)
  board[1,] <- c("/", 1:n)
  players <- c("X", "O")
  
  # start game message
  cat("Welcome to tic-tac-toe! Press <esc> to exit game at any time.\n\n")
  write.table(format(board, justify="centre"), quote=F, row.names=F, col.names=F, file="")
  ttt.status <- list(win = 0, msg = "No one", me = "X", turn.player = TRUE)  # default player starts
  
  resp.in <- readline(prompt="Do you want to play 'X'? (y/n): ")
  if (resp.in == "n") 
    ttt.status$turn.player <- FALSE
  
  # main loop
  while (ttt.status$win == 0) {
    
    # update board with new move
    new.pos <- ttt_move(board, ttt.status$turn.player)
    board[new.pos$row, new.pos$col] <- ttt.status$me
    write.table(format(board, justify="centre"), quote=F, row.names=F, col.names=F, file="")
    
    # check win status, need to connect n
    mat <- board[-1,-1]
    if (all(diag(mat) == ttt.status$me) | all(diag(mat[,n:1]) == ttt.status$me)) {  # check diagonals
      ttt.status$win <- 1
      ttt.status$msg <- c("Congrats, player", "Sorry, computer")[c(ttt.status$turn.player,!ttt.status$turn.player)]
    }
    for (i in 1:n) {
      if (all(mat[i,] == ttt.status$me) | all(mat[,i] == ttt.status$me)) {  # check rows and cols
        ttt.status$win <- 1
        ttt.status$msg <- c("Congrats, player", "Sorry, computer")[c(ttt.status$turn.player,!ttt.status$turn.player)]
      }
    }
    
    # check if board is full
    if (sum(mat == ".") == 0)
      ttt.status$win <- 1
    
    # update status for next turn
    ttt.status$me <- players[!players %in% ttt.status$me]
    ttt.status$turn.player <- !ttt.status$turn.player
  }
  message(paste("Game over.", ttt.status$msg, "wins!!"))  
}

ttt_move <- function(mat, turn.p) {
  pos.next <- list(row = 0, col = 0)
  if (turn.p == TRUE) {  
    message("Your move!")
    pos.next$row <- as.numeric(readline(prompt="Enter the row ID of where you'd like to move: ")) + 1
    pos.next$col <- as.numeric(readline(prompt="Enter the column ID of where you'd like to move: ")) + 1
  } 
  else { 
    Sys.sleep(0.5)
    message("Computer move!")
    Sys.sleep(0.5)
    
    # naive AI: pick random empty spot
    empty <- which(mat==".", arr.ind=T)
    move.random <- empty[sample(1:nrow(empty), 1),]
    pos.next$row <- move.random[1]
    pos.next$col <- move.random[2]
  }
  return(pos.next)
}