in reply to No Iterators Allowed

I'm probably missing something but ... fringe of a list (containing string/numbers and lists containing strins/numbers and lists containing ...) are the strings/numbers in a totally flattened list, right? So the samefringe() function should check that the list contains the same strings/numbers in the same order disregarding the structure, right? Without creating the totally flattened lists, right? (Sorry I got lost in the maze so I have no idea whether you do or don't create some lists like that or modify the data structure along the way.)

use strict;
use warnings;

sub samefringe {
    my ($x, $y) = @_;
    my ($ix, $iy) = (0,0);
    samefringe_r($x, $y, $ix, $iy) and $#{$x}+1 == $ix and $#{$y}+1 ==
+ $iy;
}

sub samefringe_r {
    my ($x, $y, $ix, $iy) = @_;

    while ($ix <= $#{$x} and $iy <= $#{$y}) {
        if (ref($x->[$ix])) {
            my $i_ix = 0;
            samefringe_r( $x->[$ix], $y, $i_ix, $iy) or return;
            $ix++;
        } elsif (ref($y->[$iy])) {
            my $i_iy = 0;
            samefringe_r( $x, $y->[$ix], $ix, $i_iy) or return
            $iy++;
        } elsif ($x->[$ix] ne $y->[$iy]) {
            return
        } else {
            $ix++;
            $iy++;
        }
    }
    $_[2]=$ix;$_[3]=$iy;
    return 1;
}

my $l1 = [ "a", [qw(b c)], "d" ];
my $l2 = [ qw(a b c d) ];
my $l3 = [ qw(a b c d e)];
my $l4 = [ qw(a x c d)];

print "1 x 2, should be same : ".(samefringe($l1, $l2) ? 'same' : 'dif
+f')."\n";

print "1 x 3, should be diff : ".(samefringe($l1, $l3) ? 'same' : 'dif
+f')."\n";
print "1 x 4, should be diff : ".(samefringe($l1, $l4) ? 'same' : 'dif
+f')."\n";
print "2 x 3, should be diff : ".(samefringe($l2, $l3) ? 'same' : 'dif
+f')."\n";
print "2 x 4, should be diff : ".(samefringe($l2, $l4) ? 'same' : 'dif
+f')."\n";

[download]

Jenda
Support Denmark!
Defend the free world!

Replies are listed 'Best First'.
Re^2: No Iterators Allowed
by runrig (Abbot) on Mar 04, 2008 at 19:06 UTC
    Here's how I might have done it if I were using iterators (which uses an explicit stack that the solutions in the referenced document in the OP avoid):
    sub samefringe {
  my ( $x, $y ) = map { fringe_iter($_) } @_;
  my ( $next_x, $next_y );
  while ( 1 ) {
    ( $next_x, $next_y ) = ( $x->(), $y->() );
    last unless $next_x and $next_y;
    return unless $next_x eq $next_y;
  }
  return ( $next_y || $next_y ) ? 0 : 1;
}

sub fringe_iter {
  my $list = shift;
  my @arr = @$list;
  sub {
    while (1) {
      my $reftype = ref($arr[0]);
      return shift @arr unless $reftype;
      unshift @arr, fringe_iter(shift @arr) if $reftype eq 'ARRAY';
      my $next = $arr[0]->();
      if ( $next ) {
        unshift @arr, $next;
      } else {
        shift @arr;
      }
    }
  }
}

    [download]
[reply]
[d/l]

In Section Meditations