#!/usr/bin/perl -w
use strict;
sub tsort
{
my( %pred, %succ );
for my $av ( @_ ) {
for my $i ( 1 .. $#$av ) {
$pred{$av->[$i]}{$av->[$i-1]} ||= 1;
$succ{$av->[$i-1]}{$av->[$i]} ||= 1;
}
$succ{$av->[-1]} ||= {};
}
my @output;
while( %succ ) {
my( $best, $count );
for my $item ( keys(%succ) ) {
my $preds= keys %{$pred{$item}};
if( ! defined($count) || $preds < $count ) {
$best= $item;
$count= $preds;
last if 0 == $count;
}
}
warn "Data contains a cycle, breaking at $best.\n"
if 0 < $count;
push @output, $best;
for my $succ ( keys %{$succ{$best}} ) {
delete $pred{$succ}{$best};
}
delete $succ{$best};
}
return wantarray ? @output : \@output;
}
my @array1= ( 1, 3, 4, 6 );
my @array2= ( 1, 2, 4, 6 );
my @array3= ( 1, 2, 3, 5 );
my @output= tsort( \( @array1, @array2, @array3 ) );
print "@output\n";
@output= tsort( [1,2,3,4], [1,3,2,4] );
print "@output\n";
output is
1 2 3 4 5 6
Data contains a cycle, breaking at 2.
1 2 3 4