1 files changed, 30 insertions, 0 deletions
diff --git a/challenge-147/alexander-karelas/perl/ch2.pl b/challenge-147/alexander-karelas/perl/ch2.pl
new file mode 100755
index 0000000000..b6548da74a
--- /dev/null
+++ b/challenge-147/alexander-karelas/perl/ch2.pl
@@ -0,0 +1,30 @@
+#!/usr/bin/env perl
+
+use v5.32;
+use warnings;
+
+use experimental 'signatures';
+
+my @cache;
+my %cache;
+sub get_nth_pentagon_number ($n) {
+    my $pentagon = $cache[$n];
+    $pentagon //= do {
+        $cache[$n] = $n * (3 * $n - 1) / 2;
+        $cache{ $cache[$n] } = $n;
+    }
+}
+
+for (my $i = 1; ; $i++) {
+    my $ith = get_nth_pentagon_number($i);
+    get_nth_pentagon_number(2 * $i - 1);
+    get_nth_pentagon_number(2 * $i);
+    for (my $j = 1; $j < $i; $j++) {
+        my $jth = get_nth_pentagon_number($j);
+        if (exists $cache{$ith + $jth} and exists $cache{$ith - $jth}) {
+            say "P($i) + P($j) = $ith + $jth = @{[ $ith + $jth ]} = P(", $cache{$ith + $jth}, ")";
+            say "P($i) - P($j) = $ith - $jth = @{[ $ith - $jth ]} = P(", $cache{$ith - $jth}, ")";
+            exit;
+        }
+    }
+}