Question

USING RSTUDIO: Write a script that allows two people to play tic-tac-toe. The script should allow each player to take sequential turns and to interactively enter their choice of position at the command line on each turn. For each turn, the script should output the set-up of the board. Note, you don’t have to use “x” and “o” as the symbol of each player. Note, the main body of this code (not including functions) should be able to be written in less than 30 lines.

Answer 1

# 1. Draw tic-tac-toe board.
# 2. Add a playing loop and a board variable.
# 3. Alternate player ("X", "O") and require move on empty.
# 4. Check for win.
# 5. Add random computer player.
rm(list=ls()) # clear all defined objects

# Return whether player has 3 in a row on board.
won = function(board, player) {
for (row in 1:3) {
if (sum(board[row, ] == player) == 3) { # win in row
return(TRUE)
}
}
# ... check the 3 columns
# ... check the two 2 diagonals
return(FALSE)
}
# Here are a few test cases. Add a few more.
board = matrix(c("X","O","E","X","O","E","X","E","E"),
nrow=3, ncol=3)
stopifnot( won(board, "X"))
stopifnot(!won(board, "O"))

# ---------- Here's the main program ----------
par(pty="s") # square plot type
x = rep(1:3, each = 3)
y = rep(1:3, times = 3)
symbols(x, y, squares=rep(1, times=9),
inches=FALSE, # match squares to axes
xlim=c(0,4),
ylim=c(4,0)) # flip y axis to match matrix format
board = matrix(rep("E", times=9), nrow=3, ncol=3)

player = "X"
for (i in 1:9) { # loop through 9 turns
if (player == "X") {
repeat { # get user input on empty square
index = identify(x, y, n=1, plot=FALSE)
row = y[index]
col = x[index]
if (board[row, col] == "E") {
break
}
}
} else { # computer chooses random empty square
open.indices = which(c(board)=="E")
index = sample(x=open.indices, size=1)
row = y[index]
col = x[index]
}
board[row, col] = player
text(x=x[index], y=y[index], labels=player)
print(board)
if (won(board, player)) {
text(x=2, y=.2, labels=paste(player, "won!"), col="red")
break
}
player = ifelse(player == "X", "O", "X")
}