#!/usr/bin/perl -w
use strict;
use Algorithm::Loops qw(NestedLoops);
use List::Util qw(sum);

#Set no. of elements, frequencies and the sum value
my $nElements = 2;
my @freq = qw (0.1 0.2 0.7);
my $targetSum = 4;

#Ways of generating sum given no. of elements
my @pos = (0..$#freq);
my (@combo, @matrix);
for my $c (0..$nElements-1) {
	push @combo, [@pos];
	}
my @nest = NestedLoops(\@combo, sub { [ @_ ] } );
for my $n (0..$#nest) {
	push @{$matrix[sum @{$nest[$n]}]}, join ('', @{$nest[$n]});
	}
my @ways = @{$matrix[$targetSum]};

#Now calculate P-value
my @pVal;
foreach my $w (0..$#ways) {
	my @f = split ('', $ways[$w]);
	#print "@f\n";
	my $p = $freq[$f[0]];
	#print $p,"\n";
	for my $g (1..$#f) {
		$p *= $freq[$f[$g]];
		}
	push @pVal, $p;
	}
my $pVal = sum @pVal;
print "P-value(sum of $nElements = $targetSum) = $pVal\n";

#Prints: P-value(sum of 2 = 4) = 0.49