use strict;
use Data::Dumper;

my @in = ( [qw(M N)],
           [qw(M N P O)],
           [qw(C B A)],
           [qw(U S)],
           [qw(V T)],
           [qw(C G F E D)],
           [qw(C G F H)],
           [qw(C G F H I)],
           [qw(C G F H J)],
           [qw(M K)]
         );

sub arrayCompare {
    my @a = @$a;
    my @b = @$b;

    while ( 1 )
    {
        return 0 if @a ==0 && @b == 0;
        return -1 if @a == 0;
        return 1 if @b == 0;
        my $cmp = $a[0] cmp $b[0];
        return $cmp if $cmp != 0;
        shift @a; shift @b;
    }
}

my @out = sort arrayCompare @in;

print Dumper @out;