Problem 26, Perl 5.

026.pl

@@ -0,0 +1,33 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use 5.010;
+use List::MoreUtils qw(any firstidx);
+
+sub recurring_cycle_length {
+    my ( $numerator, $denominator ) = @_;
+
+    my ( @remainders, $remainder );
+
+    while (1) {
+        while ( $denominator > $numerator ) { $numerator *= 10 }
+        if ( $remainder = $numerator % $denominator ) {
+            last if any { $_ == $remainder } @remainders;
+            push @remainders, $remainder;
+            $numerator = $remainder;
+        }
+        else {
+            last;
+        }
+    }
+
+    return 0 unless @remainders && $remainder;
+
+    return scalar(@remainders) - firstidx { $_ == $remainder } @remainders;
+}
+
+#say for map { $_ . ' ' . recurring_cycle_length( 1, $_ ) } 2 .. 9;
+
+my @lengths = sort { $a->[1] <=> $b->[1] }
+    map { [ $_, recurring_cycle_length( 1, $_ ) ] } 2 .. 999;
+say $lengths[-1]->[0];