sub parts {
    my ( $cnt, $ra_out, $ra_val, $ra_in ) = @_;
    if( $#$ra_val != $cnt ){ #working array not full
        if( $#$ra_in > -1 ){ #fill it up
            push(@$ra_val, shift(@$ra_in));
            parts( $cnt, $ra_out, $ra_val, $ra_in );
        } else {             #done with list
            return;
        }
   } else {
        push(@$ra_out, join('',@$ra_val));                #add to output array, joined ltr string
        shift(@$ra_val);                                  #rip off first ltr
        push(@$ra_val, shift(@$ra_in)) if($#$ra_in > -1); #add new ltr, if any remaining
        parts( $cnt, $ra_out, $ra_val, $ra_in );
    }
}
my @in  = split( '', "computer" ); # input array of individual letters
my @out;                           # out array of strings each of $cnt+1 ltrs
my @val;                           # working array of individual letters, $cnt+1 elements
parts( 2, \@out, \@val, \@in );
#results in @out