solution to task 1

1 files changed, 45 insertions, 0 deletions

diff --git a/challenge-076/jo-37/perl/ch-1.pl b/challenge-076/jo-37/perl/ch-1.pl
new file mode 100755
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+++ b/challenge-076/jo-37/perl/ch-1.pl
@@ -0,0 +1,45 @@
+#!/usr/bin/perl
+
+use Test2::V0;
+use Math::Prime::XS 'is_prime';
+use bigint;
+
+# The task states:
+#	"find the minimum number of prime numbers required, whose summation
+# 	gives you $N".
+# This does not imply finding specific summands, IMHO.
+#
+# According to Goldbach's conjecture, every even number greater than two
+# can be expressed as the sum of two primes.  As there is no exception to
+# this rule for $n <= 4e18, it may be considered as valid for this task.
+sub num_prime_summands {
+	my ($n) = @_;					# keep @_
+	$_[1] = 2;						# provide default retcode
+
+	return 0 if $n < 2;				# not a sum of primes
+	return 1 if $n == 2;			# 2 is prime
+	goto &assure if $n % 2 == 0;	# Goldbach's conjecture
+	return 1 if is_prime $n;		# $n is prime
+	return 2 if is_prime $n - 2;	# $n - 2 is prime
+
+	$_[1]++; goto &assure;			# Else: $n minus any odd prime is even,
+									# where Goldbach's conjecture is
+									# applied again.
+}
+
+# Warn about results that cannot be assured.
+sub assure {
+	my ($n, $r) = @_;
+	warn "The result is not assured!\n" if $n > 4e18;
+
+	$r;
+}
+
+
+is num_prime_summands($_->[0]), $_->[1]
+	foreach [1, 0], [2, 1], [3, 1], [4, 2], [5, 1], [6, 2], [7, 1],
+		[8, 2], [9, 2], [10, 2], [11, 1], [12, 2], [13, 1], [14, 2],
+		[15, 2], [16, 2], [17, 1], [18, 2], [19, 1], [20, 2], [21, 2],
+		[22, 2], [23, 1], [24, 2], [25, 2], [26, 2], [27, 3], [28, 2];
+
+done_testing;