#!/usr/bin/perl -w

use strict;

exit main();

# This is not tilly's recommended test for how random an
# ordering is.  Repeatedly give a sorted list of numbers
# (if not using numbers, swap the < line for the "lt"
# line) to your randomizer and pass the results to
# cntincseq().  If your randomizer is good, then
# cntincseq() will return values that are distributed
# around something close to ( list size / 2 ).
sub cntincseq (\@) {
    my( $aList )= @_;
    my %seq;
    @seq{ 0..$#{$aList} }= @$aList;
    my( $idx, $cnt )= 0..1;
    while(  ++$idx < @$aList  ) {
        $cnt++  if  $seq{$idx} < $seq{$idx-1}
#       $cnt++  if  $seq{$idx} lt $seq{$idx-1}
    }
    return $cnt;
}

sub validate ($&$) {
    my( $cnt, $munge, $size )= @_;
    my @counts;
    for(  1..$cnt  ) {
        my @list= 1..$size;
        &$munge( \@list );
        push @counts, cntincseq( @list );
        print " ",$counts[-1];
    }
    return @counts;
}

sub fy {
    my( $aList )= @_;
    for(  reverse 2..@$aList  ) {
        my $i= rand($_);
        @$aList[$_-1,$i]= @$aList[$i,$_-1];
    }
}

sub hash {
    my %hash;
    for(  @{$_[0]}  ) {
        $hash{rand()}= $_;
    }
    @{$_[0]}= values %hash;
}

sub main {
    $|= 1;
    my $tot;
    my @counts= validate( 10, \&fy, 10000 );
    # And here we have a particularly nasty abuse
    # of C<map> for entertainment purposes only.
    # Do not use in production code!
    print "\nFisher-Yates: ",
        ($tot=0,map{$tot+=$_}@counts)[-1]/@counts, "\n";
    @counts= validate( 10, \&hash, 10000 );
    print "\nTye hash: ",
        ($tot=0,map{$tot+=$_}@counts)[-1]/@counts, "\n";
    return 0;
}