#!perl
use strict;
use warnings;

my %counter;

#bags are represented by an array.
#marbles are represented by strings describing their colour

{my @bag = (["red", "red"],
            ["red", "black"],
            ["black", "black"]);

    sub random_bag {
        my     $choice = rand();
        if    ($choice < 0.33333) {return $bag[0];}
        elsif ($choice < 0.66667) {return $bag[1];}
        else                      {return $bag[2];}}}

#The next function picks a random bag then removes the first marble
#colour from the array if the random function returns a value lower
#than 0.5, else the second marble colour is removed. The colour of
#this marble is then concatened with the colour of the remaining
#marble, thus forming a key for a hash-value, which is then increased
#by 1.

sub random_marbles {
    my @marble = @{random_bag()};
    if (rand() < 0.5){
        $counter{ shift(@marble).$marble[0] }++}
    else {
        $counter{ pop  (@marble).$marble[0] }++}}

my $experiments = 0;

EXPERIMENT: while ($experiments < 10000) {
                 random_marbles();
            next EXPERIMENT}

            continue {
                 $experiments++;}    

print "In $counter{\"redred\"} cases both the first as well as the second marble were red \n";
print "In $counter{\"redblack\"} cases the second marble was black while the first one was red \n";
print "In $counter{\"blackred\"} cases the second marble was red while the first one was black \n";
print "In $counter{\"blackblack\"} cases both the first as well as the second marble were black. \n";
print "In ", $counter{"redred"}/($counter{"redred"}+$counter{"redblack"}) * 100, "% of the cases, the 2nd marble was red if the first one was red. \n";