flip.pl

#!/usr/bin/env perl

use strict;
use warnings;

my $flips = shift @ARGV // 1000;

print "I'm going to flip a coin [$flips] times...\n";

my @thresholds = (5, 10);

my $max;

my @results;

push @results, rand for 1..$flips;

my $t_run;
my $h_run;
my %count;
my %runs;
my $first_flip = shift @results;
my $last_flip = $first_flip > .5 ? 'h' : 't';
if ($last_flip eq 'h') {
    $h_run = 1;
}
else {
    $t_run = 1;
}
foreach my $flip (@results) {
    my $th = 't';
    $th = 'h' if $flip > .5;
    $count{$th}++;
    if ($t_run and $th eq 't') {
        $t_run++;
    }
    if ($h_run and $th eq 'h') {
        $h_run++;
    }
    if ($last_flip ne $th) {
        # a run has just ended
        $runs{$h_run}++ if $h_run;
        $runs{$t_run}++ if $t_run;
        $h_run = $t_run = 0;
        $h_run = 1 if $th eq 'h';
        $t_run = 1 if $th eq 't';
    }

    $last_flip = $th;
}
$runs{$h_run}++ if $h_run;
$runs{$t_run}++ if $t_run;

#print Dumper(\%runs); use Data::Dumper;
my @runs_in_order = sort {$a <=> $b} keys %runs;

foreach my $run_length (@runs_in_order) {
    print "Got a [$run_length] run [$runs{$run_length}] times\n";
}

[mjsouth@msouth-ns-air ~ ]$ ./flip.pl
I'm going to flip a coin [1000] times...
Got a [1] run [213] times
Got a [2] run [136] times
Got a [3] run [74] times
Got a [4] run [32] times
Got a [5] run [14] times
Got a [6] run [4] times
Got a [7] run [4] times
Got a [8] run [3] times
Got a [9] run [1] times
Got a [10] run [1] times
[mjsouth@msouth-ns-air ~ ]$ ./flip.pl 50
I'm going to flip a coin [50] times...
Got a [1] run [14] times
Got a [2] run [7] times
Got a [3] run [3] times
Got a [4] run [2] times
Got a [5] run [1] times