Merge pull request #6184 from PerlBoy1967/branch-for-challenge-167

w167 - Task 1

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+#!/bin/perl
+
+=pod
+
+The Weekly Challenge - 167
+ - https://theweeklychallenge.org/blog/perl-weekly-challenge-167/#TASK1
+
+Author: Niels 'PerlBoy' van Dijke
+
+Task 1: Circular Prime
+Submitted by: Mohammad S Anwar
+
+Write a script to find out first 10 circular primes having at least 3 digits (base 10).
+
+Please checkout wikipedia for more information.
+
+=cut
+
+use v5.16;
+
+use IO::File;
+use Math::Primality qw(next_prime);
+use Math::Prime::XS qw(is_prime);
+
+STDOUT->autoflush(1);
+
+my ($n, $p) = (0,0);
+
+# According to http://oeis.org/A016114 
+# should the first 19 circular primes be doable
+while ($n < 19) {
+  $p = next_prime($p);
+  if (isCircularPrime($p)) {
+    say int($p); $n++;
+  }
+}
+
+sub isCircularPrime ($) {
+  my $p = $_[0];
+
+  state $circularPrimes = {};
+
+  # Below 10 are straight circular primes
+  if (length($p) == 1) {
+    $circularPrimes->{$p}++;
+    return 1;
+  }
+
+  # If the prime contains a '5' or becomes potentionally even
+  # it can't be a circular prime
+  return 0 if ($p =~ m#[024568]#);
+
+  my ($n, $len) = ($p, length($p) - 1);
+  for (1 .. $len) {
+    $n = substr($n,1).substr($n,0,1);
+    return 0 unless (!exists $circularPrimes->{$n} && is_prime($n));
+  }
+
+  $circularPrimes->{$p}++;
+
+  return 1;
+}
+
+