#!/usr/bin/perl
use strict;
use warnings;
use List::Util qw/ shuffle /;
use Statistics::Descriptive;

my @contaminated_walks;

for (1 .. 100) {
	my $contaminated = 100;
	my $grid_rows = 100;
	my $grid_cols = 100;
	my $steps = 100;
	my $num_walks = 100;
	my @walks;
	
	for (1 .. $num_walks) {
		my @grid = # 1's and 0's randomly ordered
			shuffle( (1) x $contaminated, 
					 (0) x ($grid_rows * $grid_cols - $contaminated)
				   );
		
		# for each walk, 'grep' gets the count of contaminated cells
		push @walks, scalar grep $_, map $grid[rand @grid], 1 .. $steps;
	}
	push @contaminated_walks, scalar grep $_, @walks;
}

my $stat = Statistics::Descriptive::Sparse->new();
$stat->add_data(@contaminated_walks);

printf "mean: %.f std. deviation: %.f count: %d\n",
	$stat->mean, $stat->standard_deviation, $stat->count;

__END__
C:\Old_Data\perlp>perl my_stat.pl
mean: 64 std. deviation: 5 count: 100