#!/usr/bin/perl
use strict;
use warnings;

print longest_palindrome( 'sacascascsacascascascadvgkgjsflfjgfk' );

sub longest_palindrome {
    my %lookup;
    my ($index, $record) = (-1, 0);
    push @{ $lookup{ substr($_[0], $_, 1) } } , $_ for 0 .. (length $_[0]) - 1;
    for my $letter ( keys %lookup ) {
        my $last = $#{ $lookup{ $letter } };        
        for my $start ( 0 .. $last - 1 ) {
            for my $end ( reverse ( $start + 1 .. $last ) ) {
                my $pos = $lookup{ $letter }[ $start ];
                my $length = $lookup{ $letter }[ $end ] - $pos + 1;
                if ( $length > $record ) {
                    my $palindrome = substr($_[0], $pos, $length);
                    if ( $palindrome eq reverse $palindrome ) {
                        ($index, $record) = ($pos, $length);
                        last;
                    }
                }
            }
        }
    }
    return substr($_[0], $index, $record);
}