Solution to task 1

1 files changed, 73 insertions, 0 deletions

diff --git a/challenge-118/jo-37/perl/ch-1.pl b/challenge-118/jo-37/perl/ch-1.pl
new file mode 100755
index 0000000000..66a2391037
--- /dev/null
+++ b/challenge-118/jo-37/perl/ch-1.pl
@@ -0,0 +1,73 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0 '!float';
+use PDL;
+use Math::Prime::Util qw(fromdigits todigits);
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV == 1;
+usage: $0 [-examples] [-tests] [--] [N]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N
+    check if N in binary notation is a palindrome.
+
+EOS
+
+
+### Input and Output
+
+say 0 + !!bin_pal(shift);
+
+
+### Implementation
+
+# Check if the given integer (as string or number) in its binary
+# representation is a palindrome.
+
+sub bin_pal {
+    # Convert the given number into a byte piddle made of its binary
+    # digits.
+	my $n = byte todigits shift, 2;
+    
+    # Xor the piddle with its reverse and check that none of the
+    # resulting elements is set.
+    !any $n ^ $n->slice('-1:0');
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is bin_pal(5), T(), 'example 1';
+        is bin_pal(4), F(), 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        my @head = '1';
+        push @head, int rand 2 for 0 .. 2047;
+
+        my $n = fromdigits([@head, reverse @head], 2);
+        is bin_pal($n), T(),
+            'random 4096 bit binary palindrome';
+        is bin_pal($n - 1), F(),
+            'one off random binary palindrome';
+	}
+
+    done_testing;
+    exit;
+}