my @front, @back;
while( @array1 ) {
    if( exists $skip{$_->[0]} ) {
        push @back, $_;
    else {
        push @front, $_;
    }
}
my @array2 = (@front, @back);

##</code><code>##

    push @{exists $skip{$_->[0]} ? \@back : \@front}, $_;