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Merge pull request #859 from kbrannen/23-checkers-perl

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23 checkers perl
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Jeff Atwood
2023-05-29 09:07:00 -07:00
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commit 016fc0e635
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6
23_Checkers/perl/README.md
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Original source downloaded [from Vintage Basic](http://www.vintage-basic.net/games.html) Original source downloaded [from Vintage Basic](http://www.vintage-basic.net/games.html)
Conversion to [Perl](https://www.perl.org/) Conversion to [Perl](https://www.perl.org/)
Note: This version has lines and columns numbers to help you with choosing the cell
to move from and to, so you don't have to continually count. It also puts a "." only for
blank cells you can move to, which I think makes for a more pleasing look and makes
it easier to play. If you want the original behavior, start the program with an arg
of "-o" for the original behavior.

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23_Checkers/perl/checkers.pl Executable file
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#!/usr/bin/perl
# Checkers program in Perl
# Started with checkers.annotated.bas
# Translated by Kevin Brannen (kbrannen)
use strict;
use warnings;
# globals
#
# The current move: (rating, current x, current y, new x, new y)
# 'rating' represents how good the move is; higher is better.
my @ratings = (-99); # (4); # Start with minimum score
# The board. Pieces are represented by numeric values:
#
# - 0 = empty square
# - -1,-2 = X (-1 for regular piece, -2 for king)
# - 1,2 = O (1 for regular piece, 2 for king)
#
# This program's player ("me") plays X.
my @board; # (7,7)
# chars to print for the board, add 2 to the board value as an index to the char
my @chars = ("X*", "X", ".", "O", "O*");
my $neg1 = -1; # constant holding -1
my $winner = "";
my $upgrade = shift(@ARGV) // "";
$upgrade = $upgrade eq "-o" ? 0 : 1;
#####
print "\n";
print " " x 32, "CHECKERS\n";
print " " x 15, "CREATIVE COMPUTING MORRISTOWN, NEW JERSEY\n\n\n";
print "THIS IS THE GAME OF CHECKERS. THE COMPUTER IS X,\n";
print "AND YOU ARE O. THE COMPUTER WILL MOVE FIRST.\n";
print "SQUARES ARE REFERRED TO BY A COORDINATE SYSTEM.\n";
print "(0,0) IS THE LOWER LEFT CORNER\n";
print "(0,7) IS THE UPPER LEFT CORNER\n";
print "(7,0) IS THE LOWER RIGHT CORNER\n";
print "(7,7) IS THE UPPER RIGHT CORNER\n";
print "THE COMPUTER WILL TYPE '+TO' WHEN YOU HAVE ANOTHER\n";
print "JUMP. TYPE TWO NEGATIVE NUMBERS IF YOU CANNOT JUMP.\n";
print "ENTER YOUR MOVE POSITION LIKE '0 0' OR '0,0'.\n\n\n";
# Initialize the board. Data is 2 length-wise strips repeated.
my @data = ();
for (1 .. 32) { push(@data, (1,0,1,0,0,0,-1,0, 0,1,0,0,0,-1,0,-1)); }
for my $x (0 .. 7)
{
for my $y (0 .. 7)
{
$board[$x][$y] = shift(@data);
}
}
# Start of game loop. First, my turn.
while (1)
{
# For each square on the board, search for one of my pieces
# and if it can make the best move so far, store that move in 'r'
for my $x (0 .. 7)
{
for my $y (0 .. 7)
{
# Skip if this is empty or an opponent's piece
next if ($board[$x][$y] > -1);
# If this is one of my ordinary pieces, analyze possible
# forward moves.
if ($board[$x][$y] == -1)
{
for (my $a = -1 ; $a <= 1 ; $a +=2)
{
$b = $neg1;
find_move($x, $y, $a, $b);
}
}
# If this is one of my kings, analyze possible forward
# and backward moves.
if ($board[$x][$y] == -2)
{
for (my $a = -1 ; $a <= 1 ; $a += 2)
{
for (my $b = -1 ; $a <= 1 ; $b += 2) { find_move($x, $y, $a, $b); }
}
}
}
}
if ($ratings[0] == -99) # Game is lost if no move could be found.
{
$winner = "you";
last;
}
# Print the computer's move. (Note: chr$(30) is an ASCII RS
# (record separator) code; probably no longer relevant.)
print "FROM $ratings[1],$ratings[2] TO $ratings[3],$ratings[4] ";
$ratings[0] = -99;
# Make the computer's move. If the piece finds its way to the
# end of the board, crown it.
LOOP1240: {
if ($ratings[4] == 0)
{
$board[$ratings[3]][$ratings[4]] = -2;
last LOOP1240;
}
$board[$ratings[3]][$ratings[4]] = $board[$ratings[1]][$ratings[2]];
$board[$ratings[1]][$ratings[2]] = 0;
# If the piece has jumped 2 squares, it means the computer has
# taken an opponents' piece.
if (abs($ratings[1] - $ratings[3]) == 2)
{
$board [($ratings[1]+$ratings[3])/2] [($ratings[2]+$ratings[4])/2] = 0; # Delete the opponent's piece
# See if we can jump again. Evaluate all possible moves.
my $x = $ratings[3];
my $y = $ratings[4];
for (my $a = -2 ; $a <= 2 ; $a += 4)
{
if ($board[$x][$y] == -1)
{
$b = -2;
eval_move($x, $y, $a, $b);
}
if ($board[$x][$y] == -2)
{
for (my $b = -2 ; $b <= 2 ; $b += 4) { eval_move($x, $y, $a, $b); }
}
}
# If we've found a move, go back and make that one as well
if ($ratings[0] != -99)
{
print "TO $ratings[3], $ratings[4] ";
$ratings[0] = -99;
next LOOP1240;
}
}
} # LOOP1240
# Now, print the board
print "\n\n\n";
for (my $y = 7 ; $y >= 0 ; $y--)
{
my $line = "";
$line = "$y|" if ($upgrade);
for my $x (0 .. 7)
{
my $c = $chars[$board[$x][$y] + 2];
$c = ' ' if ($upgrade && (($y % 2 == 0 && $x % 2 == 1) || ($y % 2 == 1 && $x % 2 == 0)));
$line = tab($line, 5*$x+7, $c);
}
print $line;
print " \n\n";
}
print " _ _ _ _ _ _ _ _\n" if ($upgrade);
print " 0 1 2 3 4 5 6 7\n" if ($upgrade);
print "\n";
# Check if either player is out of pieces. If so, announce the
# winner.
my ($z, $t) = (0, 0);
for my $x (0 .. 7)
{
for my $y (0 .. 7)
{
if ($board[$x][$y] == 1 || $board[$x][$y] == 2) { $z = 1; }
if ($board[$x][$y] == -1 || $board[$x][$y] == -2) { $t = 1; }
}
}
if ($z != 1) { $winner = "comp"; last; }
if ($t != 1) { $winner = "you"; last; }
# Prompt the player for their move.
($z, $t) = (0, 0);
my ($x, $y, $e, $h, $a, $b);
do {
($e,$h) = get_pos("FROM:");
$x = $e;
$y = $h;
} while ($board[$x][$y] <= 0);
do {
($a,$b) = get_pos("TO:");
$x = $a;
$y = $b;
} while (!($board[$x][$y] == 0 && abs($a-$e) <= 2 && abs($a-$e) == abs($b-$h)));
LOOP1750: {
# Make the move and stop unless it might be a jump.
$board[$a][$b] = $board[$e][$h];
$board[$e][$h] = 0;
if (abs($e-$a) != 2) { last LOOP1750; }
# Remove the piece jumped over
$board[($e+$a)/2][($h+$b)/2] = 0;
# Prompt for another move; -1 means player can't, so I've won.
# Keep prompting until there's a valid move or the player gives
# up.
my ($a1, $b1);
do {
($a1,$b1) = get_pos("+TO:");
if ($a1 < 0) { last LOOP1750; }
} while ($board[$a1][$b1] != 0 || abs($a1-$a) != 2 || abs($b1-$b) != 2);
# Update the move variables to correspond to the next jump
$e = $a;
$h = $b;
$a = $a1;
$b = $b1;
}
# If the player has reached the end of the board, crown this piece
if ($b == 7) { $board[$a][$b] = 2; }
# And play the next turn.
}
# Endgame:
print "\n", ($winner eq "you" ? "YOU" : "I"), " WIN\n";
exit(0);
###########################################
# make sure we get a 2 value position
sub get_pos
{
my $prompt = shift;
my ($p1, $p2);
do {
print "$prompt ";
chomp(my $ans = <>);
($p1,$p2) = split(/[, ]/, $ans);
} while (!defined($p1) || !defined($p2) || $p1 < -1 || $p2 < -1 || $p1 > 7 || $p2 > 7);
return ($p1,$p2);
}
# deal with basic's tab() for line positioning
# line = line string we're starting with
# pos = position to start writing
# s = string to write
# returns the resultant string, which might not have been changed
sub tab
{
my ($line, $pos, $str) = @_;
my $len = length($line);
# if curser is past position, do nothing
if ($len <= $pos) { $line .= " " x ($pos - $len) . $str; }
return $line;
}
# Analyze a move from (x,y) to (x+a, y+b) and schedule it if it's
# the best candidate so far.
sub find_move
{
my ($x, $y, $a, $b) = @_;
my $u = $x+$a;
my $v = $y+$b;
# Done if it's off the board
return if ($u < 0 || $u > 7 || $v < 0 || $ v> 7);
# Consider the destination if it's empty
eval_jump($x, $y, $u, $v) if ($board[$u][$v] == 0);
# If it's got an opponent's piece, jump it instead
if ($board[$u][$v] > 0)
{
# Restore u and v, then return if it's off the board
$u += $a;
$v += $b;
return if ($u < 0 || $v < 0 || $u > 7 || $v > 7);
# Otherwise, consider u,v
eval_jump($x, $y, $u, $v) if ($board[$u][$v] == 0);
}
}
# Evaluate jumping (x,y) to (u,v).
#
# Computes a score for the proposed move and if it's higher
# than the best-so-far move, uses that instead by storing it
# and its score in @ratings.
sub eval_jump
{
my ($x, $y, $u, $v) = @_;
# q is the score; it starts at 0
my $q = 0;
# +2 if it promotes this piece
$q += 2 if ($v == 0 && $board[$x][$y] == -1);
# +5 if it takes an opponent's piece
$q += 5 if (abs($y-$v) == 2);
# -2 if the piece is moving away from the top boundary
$q -= 2 if ($y == 7);
# +1 for putting the piece against a vertical boundary
$q++ if ($u == 0 || $u == 7);
for (my $c = -1 ; $c <= 1 ; $c += 2)
{
next if ($u+$c < 0 || $u+$c > 7 || $v+$neg1 < 0);
# +1 for each adjacent friendly piece
if ($board[$u+$c][$v+$neg1] < 0)
{
$q++;
next;
}
# Prevent out-of-bounds testing
next if ($u-$c < 0 || $u-$c > 7 || $v-$neg1 > 7);
# -2 for each opponent piece that can now take this piece here
$q -= 2 if ($board[$u+$c][$v+$neg1] > 0 && ($board[$u-$c][$v-$neg1] == 0 || ($u-$c == $x && $v-$neg1 == $y)));
}
# Use this move if it's better than the previous best
if ($q > $ratings[0])
{
$ratings[0] = $q;
$ratings[1] = $x;
$ratings[2] = $y;
$ratings[3] = $u;
$ratings[4] = $v;
}
}
# If (u,v) is in the bounds, evaluate it as a move using
# the sub at 910, so storing eval in @ratings.
sub eval_move
{
my ($x, $y, $a, $b) = @_;
my $u = $x+$a;
my $v = $y+$b;
return if ($u < 0 || $u > 7 || $v < 0 || $v > 7);
eval_jump($x, $y, $u, $v) if ($board[$u][$v] == 0 && $board[$x+$a/2][$y+$b/2] > 0);
}