#! perl -slw
use strict;
use List::Util qw[ max ];

our $N;

use enum qw[ LEFT RIGHT ];
sub _traverse {
    my( $code, $tree, $d, $w ) = @_;

    ref $tree->[LEFT]
        and $w = _traverse( $code, $tree->[LEFT], $d+1, $w )
        or  $code->( ++$w, $d, $tree->[LEFT] );

    $code->( ++$w, $d,'^' );

    ref $tree->[RIGHT]
        and $w = _traverse( $code, $tree->[RIGHT], $d+1, $w )
        or  $code->( ++$w, $d, $tree->[RIGHT] );

    return $w;
}
sub traverse(&$) { _traverse( @_, 0, 0 ); }

use enum qw[ WIDTH DEPTH NAME ];
sub dumpTree {
    my $tree = shift;
    my @g;
    traverse{ push @g, [ @_ ]; } $tree;

    my $width = max( map $_->[WIDTH], @g );
    my $depth = max( map $_->[DEPTH], @g );
    my @graph = map ' ' x $width, 0 .. $depth;
    substr $graph[ $_->[DEPTH] ], $_->[WIDTH], 1, substr($_->[NAME],0,1) for @g;
    unshift @graph, (' ' x $width) x 2;

    for my $i ( reverse 0 .. $#graph ) {
        substr( $graph[$i-1], $-[1], $+[1]-$-[1], '/' . ' ' x (length($1)-2) . '\\' ),
        substr( $graph[ $i ], $-[2], 1, ' ' )
            while $graph[ $i ] =~ m[(\S\s*(\^)\s*\S)]g;
    }
    my $n;
    for my $i ( reverse 0 .. $#graph ) {
        $n = $+[1]-$-[1],
        substr( $graph[ $i-1 ], $-[1]+1, $n-2, '_' x ($n-2))
           while $graph[ $i ] =~ m[(/\s+\\)]g;
    }
    print for @graph, '';
    return unless $N;
    my @names = map[ split '', reverse ], grep !/\^/, map $_->[NAME], @g;
    print for map{
        join( ' ', '', map pop @$_//' ', @names )
    } 0 .. max( map scalar @$_, @names );
}

my @a = qw[
alpha bravo charlie delta echo foxtrot golf hotel indigo
juliet kilo mike november oscar papa quebec romeo sierra
tango uniform victor whiskey xray yankee zulu
];

our $S //= 0;
srand $S if $S;
my $r;
$r = int( rand $#a ), splice @a, $r, 2, [ @a[ $r, $r+1 ]] while @a > 1;
@a = @{ $a[0] };

dumpTree( \@a );