- Added solution by Peter Campbell Smith.

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+#!/usr/bin/perl
+
+# Peter Campbell Smith - 2021-08-08
+# PWC 125 task 1
+
+use strict;
+use warnings;
+
+# A Pythagorean triple consist of 3 positive integers such that
+# a**2 + b**2 = c**2. Note that a cannot equal b as sqrt(2a**2) =
+# a * sqrt(2) which cannot be integer.
+ 
+# We are asked to find all the triples where one of a, b, c equals
+# a given number n.
+
+# Clearly a < c and b < c, and we can require a < b to avoid 
+# duplicates such a 3, 4, 5 and 4, 3, 5.
+
+my ($a, $b, $c, $n, $s, @solutions);
+
+# input n
+print qq[n: ];
+$n = <>;
+chomp($n);
+
+# If c == n:
+# a < b so a**2 < n**2 / 2, so we only need to test values of a < sqrt(n**2 / 2)
+# and solutions are where n**2 - a**2 is an integer square (ie b**2)
+
+for $a (1 .. int(sqrt($n**2 / 2))) {
+	$solutions[$s++] = qq[    ($a, $b, $n)\n] if $b = is_a_square($n**2 - $a**2);
+}
+
+# If a == n:
+# We are looking for b and c such that c**2 - b**2 == n**2.  
+# if t == s + 1 then t**2 - s**2 is 2s + 1, so we only
+# need to test values of b where 2b + 1 < n**2
+# and solutions are where n**2 - b**2 is an integer square (ie a**2)
+
+for $b (1 .. 2**32) {
+	last if 2 * $b + 1 > $n**2;
+	$solutions[$s++] = qq[    ($n, $b, $c)\n] if $c = is_a_square($n**2 + $b**2);	
+}
+
+# solutions
+print qq[Input: \$N = $n\nOutput:\n];
+for $s (@solutions) { print $s };
+print qq[-1\n] unless (scalar @solutions);
+
+#---
+
+sub is_a_square {
+	my $test = sqrt($_[0]);
+	return $test == int($test) ? $test : 0;
+}