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#!/usr/bin/env perl
##############################################################################
# Perl Weekly Challenge #119
##############################################################################
#
# Task #2 - Sequence without 1-on-1
#
# Write a script to generate sequence starting at 1. Consider the increasing
# sequence of integers which contain only 1’s, 2’s and 3’s, and do not have
# any doublets of 1’s like below. Please accept a positive integer $N and
# print the $Nth term in the generated sequence.
#
# > 1, 2, 3, 12, 13, 21, 22, 23, 31, 32, 33, 121, 122, 123, 131, …
#
##############################################################################
use strict;
use warnings;
use v5.10;
use Test::More;
if (@ARGV) {
say get_nth_term_in_sequence(@ARGV);
}
else {
my @tests = (
{ input => 1, output => 1, },
{ input => 2, output => 2, },
{ input => 3, output => 3, },
{ input => 4, output => 12, },
{ input => 5, output => 13, },
{ input => 6, output => 21, },
{ input => 7, output => 22, },
{ input => 8, output => 23, },
{ input => 9, output => 31, },
{ input => 10, output => 32, },
{ input => 11, output => 33, },
{ input => 12, output => 121, },
{ input => 13, output => 122, },
{ input => 14, output => 123, },
{ input => 15, output => 131, },
{ input => 16, output => 132, },
{ input => 17, output => 133, },
{ input => 18, output => 212, },
{ input => 60, output => 2223, },
{ input => 200, output => 31221, },
{ input => 1000, output => 1332223, },
);
for my $test (@tests) {
my $output = get_nth_term_in_sequence( $test->{'input'} );
is( $output, $test->{'output'} );
}
done_testing();
}
exit;
##############################################################################
#
# This is just a basic bruteforce implementation, but it works.
#
##############################################################################
sub get_nth_term_in_sequence {
my $N = shift;
my $term = 0;
while ( $N > 0 ) {
$term++;
$N-- if ( $term =~ /^[123]+$/ && $term !~ /11/ );
}
return $term;
}
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