sub mutate{
    my @string = @{$_[0]};
    for my $i (0.. $#string){
        my $aref = $string[$i];
        #print "\n";
        if (rand() < $mutation_rate){
            my $position1 = int(rand($#{$aref}));
            my $position2 = int(rand($#{$aref}));
            if ($position1 ne $position2){
                my $temp = $string[$i][$position1];
                $string[$i][$position1] = $string[$i][$position2];
                $string[$i][$position2] = $temp;
            }		
        }
    }
    return \@string;
}


##</code><code>##

sub mutate{
    my @string = @{ $_[ 0 ] };
    for my $i ( 0 .. $#string ){
        my $aref = $string[ $i ];
        #print "\n";
        if ( rand() < $mutation_rate ){
            my $position1 = int rand @$aref;
            my $position2 = int rand @$aref;

            if ( $position1 != $position2 ){
                @{ $string[ $i ] }[ $position1, $position2 ] = @{ $string[ $i ] }[ $position2, $position1 ];
            }		
        }
    }
    return \@string;
}