#! perl -slw
use strict;
use 5.010;
use threads::Gather;
use Scalar::Util qw[ dualvar ];
use constant { TRUE => dualvar( 1, 'true' ), FALSE => dualvar( 0, 'false' ) };
use enum qw[ LEFT RIGHT ];

sub fringe {
    my $tree = shift;
    gather{
        my $t = shift;
        !ref( $t ) and return take( $t );
        $^R->( $t->[LEFT]  );
        $^R->( $t->[RIGHT] );
    } 1, $tree;
}

sub sameFringe {
    my @i = map fringe( $_ ), @_;
    for( my @v = map &$_, @i; defined( $v[0] // $v[1] ); @v = map &$_,@i ) {
        local $^W; $v[0] == $v[1] or return FALSE;
    }
    return TRUE;
}

my $a = [ 1, [ 2, [ 3, [ 4, 5 ] ] ] ];
my $b = [ 1, [ [ 2, 3 ], [ 4, 5 ] ] ];
my $c = [ [ [ [ 1, 2 ], 3 ], 4 ], 5 ];

print sameFringe( $a, $a );
print sameFringe( $a, $b );
print sameFringe( $a, $c );

my $x = [ 1, [ 2, [ 3, [ 4, [ 5, 6 ] ] ] ] ];
my $y = [ 0, [ [ 2, 3 ], [ 4, 5 ] ] ];
my $z = [ 1, [ 2, [ [ 4, 3 ], 5 ] ] ];

print sameFringe( $a, $x );
print sameFringe( $a, $y );
print sameFringe( $a, $z );

__END__
C:\test>sameFringe
true
true
true
false
false
false