#!/usr/bin/env perl

use 5.012;
use Test::More;

sub find_substring
{
	my $input  = shift;
	my $length = length $input;
	
	for my $i (1 .. $length)
	{
		my $possible = substr($input, 0, $i);
		my $repeated = $possible x (1 + int($length / $i));
		return $possible if $input eq substr($repeated, 0, $length);
	}
	
	return "";
}

my %eg = (
	abcdabcdabcdabcdab          => "abcd",
	abcdabcdabceabcdabcdabceab  => "abcdabcdabce",
	aaaabaaaabaaaaabaaaab       => "aaaabaaaaba",
);

for my $input (sort keys %eg)
{
	my $expected = $eg{$input};
	my $got      = find_substring($input);
	
	is($got, $expected, "result is '$expected' given input '$input'");
}

done_testing;