Week 321 - Moving backwards

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diff --git a/challenge-321/peter-campbell-smith/blog.txt b/challenge-321/peter-campbell-smith/blog.txt
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+http://ccgi.campbellsmiths.force9.co.uk/challenge/321
diff --git a/challenge-321/peter-campbell-smith/perl/ch-1.pl b/challenge-321/peter-campbell-smith/perl/ch-1.pl
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+++ b/challenge-321/peter-campbell-smith/perl/ch-1.pl
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+#!/usr/bin/perl
+
+# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge
+
+use v5.26;    # The Weekly Challenge - 2025-05-12
+use utf8;     # Week 321 - task 1 - Distinct average
+use warnings; # Peter Campbell Smith
+binmode STDOUT, ':utf8';
+use Encode;
+
+distinct_average(1, 2, 4, 3, 5, 6);
+distinct_average(0, 2, 4, 8, 3, 5);
+distinct_average(7, 3, 1, 0, 5, 9);
+
+# larger example
+my @numbers;
+push @numbers, int(rand(100)) for 0 .. 99;
+distinct_average(@numbers);
+
+sub distinct_average {
+	
+	my (@numbers, $j, %sums, $count);
+	
+	@numbers = @_;
+	say qq[\nInput:  (] . join(', ', @numbers) . q[)];
+	
+	# sort numbers and sum them pairwise from each end
+	@numbers = sort {$a <=> $b}  @numbers;
+	$sums{$numbers[$_] + $numbers[$#numbers - $_]} = 1 for 0 .. @numbers / 2;
+	
+	# count the number of unique sums
+	$count ++ for keys %sums;
+	
+	say qq[Output: $count];
+}
diff --git a/challenge-321/peter-campbell-smith/perl/ch-2.pl b/challenge-321/peter-campbell-smith/perl/ch-2.pl
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+++ b/challenge-321/peter-campbell-smith/perl/ch-2.pl
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+#!/usr/bin/perl
+
+# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge
+
+use v5.26;    # The Weekly Challenge - 2025-05-12
+use utf8;     # Week 321 - task 2 - Backspace compare
+use warnings; # Peter Campbell Smith
+binmode STDOUT, ':utf8';
+use Encode;
+
+backspace_compare('ab#c', 'ad#c');
+backspace_compare('ab##', 'a#b#');
+backspace_compare('same', 'same');
+backspace_compare('#same', '#same');
+backspace_compare('a#b', 'c');
+backspace_compare('the curfewww## tolls the knelllll### of paaaaa####rting day', 
+				  'z#the curfew tollxx##s the knell ofzzz### parting dayw#');
+
+sub backspace_compare {
+	
+	my ($string1, $string2, $z, $s);
+	
+	# initialise
+	($string1, $string2) = @_;
+	say qq[\nInput:  \$string1 = '$string1',\n        \$string2 = '$string2'];
+	
+	# repeatedly delete backspace and preceding character
+	for $s ($string1, $string2) {
+		$z = 1;
+		$z = ($s =~ s|.#||) while $z;
+	}
+	
+	# report
+	say qq[Output: ] . ($string1 eq $string2 ? qq[true -     '$string1'] : 
+		qq[false -    '$string1' vs '$string2']);
+}