From 675e6d67fa70096adead69caa72ca697a604f12a Mon Sep 17 00:00:00 2001
From: Peter Campbell Smith <pj.campbell.smith@gmail.com>
Date: Tue, 6 Aug 2024 13:12:55 +0100
Subject: Week 281 - Anyone for chess?

---
 challenge-281/peter-campbell-smith/blog.txt     |  1 +
 challenge-281/peter-campbell-smith/perl/ch-1.pl | 24 +++++++
 challenge-281/peter-campbell-smith/perl/ch-2.pl | 84 +++++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 challenge-281/peter-campbell-smith/blog.txt
 create mode 100755 challenge-281/peter-campbell-smith/perl/ch-1.pl
 create mode 100755 challenge-281/peter-campbell-smith/perl/ch-2.pl

diff --git a/challenge-281/peter-campbell-smith/blog.txt b/challenge-281/peter-campbell-smith/blog.txt
new file mode 100644
index 0000000000..d05f459565
--- /dev/null
+++ b/challenge-281/peter-campbell-smith/blog.txt
@@ -0,0 +1 @@
+http://ccgi.campbellsmiths.force9.co.uk/challenge/281
diff --git a/challenge-281/peter-campbell-smith/perl/ch-1.pl b/challenge-281/peter-campbell-smith/perl/ch-1.pl
new file mode 100755
index 0000000000..174a96ba56
--- /dev/null
+++ b/challenge-281/peter-campbell-smith/perl/ch-1.pl
@@ -0,0 +1,24 @@
+#!/usr/bin/perl
+
+# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge
+
+use v5.26;    # The Weekly Challenge - 2024-08-05
+use utf8;     # Week 281 - task 1 - Check color
+use warnings; # Peter Campbell Smith
+binmode STDOUT, ':utf8';
+
+check_color('d3');
+check_color('g5');
+check_color('a1');
+check_color('h8');
+
+sub check_color {
+	
+	my ($col, $row) = $_[0] =~ m|(.)(.)|;
+	
+	# convert column letter to number (0-7), multiply by
+	# row number and odd results are light, even ones dark	
+
+	printf(qq[\nInput:  \$square = '%s'\n], $col . $row);
+	printf(qq[Output: %s\n], ((ord($col) - ord('a')) * $row) & 1 ? 'true' : 'false');
+}
diff --git a/challenge-281/peter-campbell-smith/perl/ch-2.pl b/challenge-281/peter-campbell-smith/perl/ch-2.pl
new file mode 100755
index 0000000000..ebabd1c3f6
--- /dev/null
+++ b/challenge-281/peter-campbell-smith/perl/ch-2.pl
@@ -0,0 +1,84 @@
+#!/usr/bin/perl
+
+# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge
+
+use v5.26;    # The Weekly Challenge - 2024-08-05
+use utf8;     # Week 281 - task 2 - Knight's move
+use warnings; # Peter Campbell Smith
+binmode STDOUT, ':utf8';
+
+knights_move('g2', 'a8');
+knights_move('g2', 'h2');
+knights_move('a1', 'h8');
+knights_move('e3', 'e4');
+
+sub knights_move {
+	
+	my (@valid_moves, $from_square, $to_square, %from, $moves, $square, $v,
+		$trace, $square2, $x, $y, $s, %m, $next_square);
+	
+	# x, y changes for valid moves
+	@valid_moves = ([-2, 1], [-1, 2], [1, 2], [2, 1], [-2, -1], [-1, -2], [1, -2], [2, -1]);
+	
+	# initialise
+	$from_square = $_[0];
+	$to_square = $_[1];
+	say qq[\nInput:  \$start = '$from_square', \$end = '$to_square'];
+	
+	for $x ('a' .. 'h') {
+		for $y (1 .. 8) {
+			$from{$x . $y} = '';
+			$m{$x . $y} = -1;
+		}
+	}
+	$from{$from_square} = 0;
+	$m{$from_square} = 0;
+	
+	# find squares $moves away from starting square
+	for $moves (1 .. 10) {
+		
+		# look at every square
+		for $s (0 .. 63) {
+			
+			# select those accessible in $moves - 1 moves
+			$square = chr(ord('a') + $s % 8) . (int($s / 8) + 1);
+			if ($m{$square} == $moves - 1) {
+				
+				# mark squares accessible from them
+				for $v (@valid_moves) {
+					$next_square = displace($square, $v);
+					next if $next_square eq 'invalid';
+					next unless $from{$next_square} eq '';
+					
+					# we've arrived!
+					if ($next_square eq $to_square) {
+						$trace = $to_square;
+						$square2 = $square;
+						while (1) {
+							$trace = $square2 . qq[ → $trace];
+							last if $square2 eq $from_square;
+							$square2 = $from{$square2};
+						} 
+						say qq[Output: $moves ($trace)];
+						return;
+					}
+					$from{$next_square} = $square;
+					$m{$next_square} = $moves;
+				}
+			}
+		}
+	}
+}
+
+sub displace {
+	
+	my (@square, $x, $y);
+	
+	# displace($square, $x, $y) returns square displaced by those increments
+	($x, $y) = $_[0] =~ m|(.)(.)|;
+	@square = @{$_[1]};
+	
+	$x = chr(ord($x) + $square[0]);
+	$y = $y + $square[1];
+	return ($x lt 'a' or $x gt 'h' or $y < 1 or $y > 8) ? 'invalid' : $x . $y;
+}	
-- 
cgit