tasks a-s

Task/Self-referential-sequence/Perl/self-referential-sequence.pl

@@ -0,0 +1,39 @@
+sub next_num {
+	my @a;
+	$a[$_]++ for split '', shift;
+	join('', map(exists $a[$_] ? $a[$_].$_ : "", reverse 0 .. 9));
+}
+
+my %cache;
+sub seq {
+	my $a = shift;
+	my (%seen, @s);
+	until ($seen{$a}) {
+		$seen{$a} = 1;
+		push(@s, $a);
+		last if !wantarray && $cache{$a};
+		$a = next_num($a);
+	}
+	return (@s) if wantarray;
+
+	my $l = $cache{$a};
+	if ($l) { $cache{$s[$_]} = $#s - $_ + $l for (0 .. $#s); }
+	else {
+		$l++ while ($s[-$l] != $a);
+		$cache{pop @s} = $l 	for (1 .. $l);
+		$cache{pop @s} = ++$l	while @s;
+	}
+	$cache{$s[0]}
+}
+
+my (@mlist, $mlen);
+for (1 .. 100_000) { # 1_000_000 takes very, very long
+	my $l = seq($_);
+	next if $l < $mlen;
+
+	if ($l > $mlen) { $mlen = $l; @mlist = (); }
+	push @mlist, $_;
+}
+
+print "longest ($mlen): @mlist\n";
+print join("\n", seq($_)), "\n\n"	for @mlist;