LDP/LDP/guide/docbook/abs-guide/nim.sh

#!/bin/bash
# nim.sh: Game of Nim

# Author: Mendel Cooper
# Reldate: 15 July 2008
# License: GPL3

ROWS=5     # Five rows of pegs (or matchsticks).
WON=91     # Exit codes to keep track of wins/losses.
LOST=92    # Possibly useful if running in batch mode.  
QUIT=99
peg_msg=   # Peg/Pegs?
Rows=( 0 5 4 3 2 1 )   # Array holding play info.
# ${Rows[0]} holds total number of pegs, updated after each turn.
# Other array elements hold number of pegs in corresponding row.

instructions ()
{
  clear
  tput bold
  echo "Welcome to the game of Nim."; echo
  echo -n "Do you need instructions? (y/n) "; read ans

   if [ "$ans" = "y" -o "$ans" = "Y" ]; then
     clear
     echo -e '\E[33;41m'  # Yellow fg., over red bg.; bold.
     cat <<INSTRUCTIONS

Nim is a game with roots in the distant past.
This particular variant starts with five rows of pegs.

1:    | | | | | 
2:     | | | | 
3:      | | | 
4:       | | 
5:        | 

The number at the left identifies the row.

The human player moves first, and alternates turns with the bot.
A turn consists of removing at least one peg from a single row.
It is permissable to remove ALL the pegs from a row.
For example, in row 2, above, the player can remove 1, 2, 3, or 4 pegs.
The player who removes the last peg loses.

The strategy consists of trying to be the one who removes
the next-to-last peg(s), leaving the loser with the final peg.

To exit the game early, hit ENTER during your turn.
INSTRUCTIONS

echo; echo -n "Hit ENTER to begin game. "; read azx

      echo -e "\033[0m"    # Restore display.
      else tput sgr0; clear
  fi

clear

}


tally_up ()
{
  let "Rows[0] = ${Rows[1]} + ${Rows[2]} + ${Rows[3]} + ${Rows[4]} + \
  ${Rows[5]}"    # Add up how many pegs remaining.
}


display ()
{
  index=1   # Start with top row.
  echo

  while [ "$index" -le "$ROWS" ]
  do
    p=${Rows[index]}
    echo -n "$index:   "          # Show row number.

  # ------------------------------------------------
  # Two concurrent inner loops.

      indent=$index
      while [ "$indent" -gt 0 ]
      do
        echo -n " "               # Staggered rows.
        ((indent--))              # Spacing between pegs.
      done

    while [ "$p" -gt 0 ]
    do
      echo -n "| "
      ((p--))
    done
  # -----------------------------------------------

  echo
  ((index++))
  done  

  tally_up

  rp=${Rows[0]}

  if [ "$rp" -eq 1 ]
  then
    peg_msg=peg
    final_msg="Game over."
  else             # Game not yet over . . .
    peg_msg=pegs
    final_msg=""   # . . . So "final message" is blank.
  fi

  echo "      $rp $peg_msg remaining."
  echo "      "$final_msg""


  echo
}

player_move ()
{

  echo "Your move:"

  echo -n "Which row? "
  while read idx
  do                   # Validity check, etc.

    if [ -z "$idx" ]   # Hitting return quits.
    then
        echo "Premature exit."; echo
        tput sgr0      # Restore display.
        exit $QUIT
    fi

    if [ "$idx" -gt "$ROWS" -o "$idx" -lt 1 ]   # Bounds check.
    then
      echo "Invalid row number!"
      echo -n "Which row? "
    else
      break
    fi
    # TODO:
    # Add check for non-numeric input.
    # Also, script crashes on input outside of range of long double.
    # Fix this.

  done

  echo -n "Remove how many? "
  while read num
  do                   # Validity check.

  if [ -z "$num" ]
  then
    echo "Premature exit."; echo
    tput sgr0          # Restore display.
    exit $QUIT
  fi

    if [ "$num" -gt ${Rows[idx]} -o "$num" -lt 1 ]
    then
      echo "Cannot remove $num!"
      echo -n "Remove how many? "
    else
      break
    fi
  done
  # TODO:
  # Add check for non-numeric input.
  # Also, script crashes on input outside of range of long double.
  # Fix this.

  let "Rows[idx] -= $num"

  display
  tally_up

  if [ ${Rows[0]} -eq 1 ]
  then
   echo "      Human wins!"
   echo "      Congratulations!"
   tput sgr0   # Restore display.
   echo
   exit $WON
  fi

  if [ ${Rows[0]} -eq 0 ]
  then          # Snatching defeat from the jaws of victory . . .
    echo "      Fool!"
    echo "      You just removed the last peg!"
    echo "      Bot wins!"
    tput sgr0   # Restore display.
    echo
    exit $LOST
  fi
}


bot_move ()
{

  row_b=0
  while [[ $row_b -eq 0 || ${Rows[row_b]} -eq 0 ]]
  do
    row_b=$RANDOM          # Choose random row.
    let "row_b %= $ROWS"
  done


  num_b=0
  r0=${Rows[row_b]}

  if [ "$r0" -eq 1 ]
  then
    num_b=1
  else
    let "num_b = $r0 - 1"
         #  Leave only a single peg in the row.
  fi     #  Not a very strong strategy,
         #+ but probably a bit better than totally random.

  let "Rows[row_b] -= $num_b"
  echo -n "Bot:  "
  echo "Removing from row $row_b ... "

  if [ "$num_b" -eq 1 ]
  then
    peg_msg=peg
  else
    peg_msg=pegs
  fi

  echo "      $num_b $peg_msg."

  display
  tally_up

  if [ ${Rows[0]} -eq 1 ]
  then
   echo "      Bot wins!"
   tput sgr0   # Restore display.
   exit $WON
  fi

}


# ================================================== #
instructions     # If human player needs them . . .
tput bold        # Bold characters for easier viewing.
display          # Show game board.

while [ true ]   # Main loop.
do               # Alternate human and bot turns.
  player_move
  bot_move
done
# ================================================== #

# Exercise:
# --------
# Improve the bot's strategy.
# There is, in fact, a Nim strategy that can force a win.
# See the Wikipedia article on Nim:  http://en.wikipedia.org/wiki/Nim
# Recode the bot to use this strategy (rather difficult).

#  Curiosities:
#  -----------
#  Nim played a prominent role in Alain Resnais' 1961 New Wave film,
#+ Last Year at Marienbad.
#
#  In 1978, Leo Christopherson wrote an animated version of Nim,
#+ Android Nim, for the TRS-80 Model I.