[euler] add solution for problem 14

Author: felher

euler/prob014-felher.pl

@@ -0,0 +1,28 @@
+use v6;
+
+# this program takes quite a few minutes on my machine
+
+my Int multi sub collatz(Int $n where * %% 2) { $n div 2;   }
+my Int multi sub collatz(Int $n             ) { 3 * $n + 1; }
+
+my Int sub get-length(Int $n)  {
+	state Int %length{Int} = 1 => 1;
+	my $result = %length{$n} // 1 + get-length collatz $n;
+	%length{$n} = $result;
+	$result;
+}
+
+my $max = 0;
+my $start = 0;
+for 1 ..^ 1_000_000 -> $n {
+	say $n; #just for progress
+	my $length = get-length $n;
+
+	if $length > $max {
+		$start = $n;
+		$max = $length;
+	}
+}
+
+say $max;
+say $start;