Week 154

3 files changed, 57 insertions, 3 deletions

diff --git a/challenge-154/cheok-yin-fung/perl/ch-1.pl b/challenge-154/cheok-yin-fung/perl/ch-1.pl
index 76313f2e6f..dd94411614 100644
--- a/challenge-154/cheok-yin-fung/perl/ch-1.pl
+++ b/challenge-154/cheok-yin-fung/perl/ch-1.pl
@@ -24,6 +24,7 @@ sub look_for {
 
     my @sw = split "", $word;
 
+    # all permutations
     my $iter = Algorithm::Permute->new(\@sw, length($word));
     my @words;
     while (my @res = $iter->next) {
@@ -31,6 +32,7 @@ sub look_for {
     }
     @words = uniqstr @words;
 
+    # use a hash to determine whether a permutation has appeared
     my %bucket = map {$_ => 0} @words;
 
     for (@collection) {
diff --git a/challenge-154/cheok-yin-fung/perl/ch-2-test-pre_calc.pl b/challenge-154/cheok-yin-fung/perl/ch-2-test-pre_calc.pl
new file mode 100644
index 0000000000..3ff75bbecc
--- /dev/null
+++ b/challenge-154/cheok-yin-fung/perl/ch-2-test-pre_calc.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/perl
+# The Weekly Challenge 154
+# Task 2 Padovan Prime
+
+use v5.22.0;
+use warnings;
+use Math::BigInt;
+
+use Math::Prime::Util qw/prime_precalc is_prime/;
+prime_precalc(10_000_000);
+
+
+
+my $NUM_OF_TERMS = $ARGV[0] || 10;
+
+my @ans = ();
+my $pdvstate = [Math::BigInt->new(1), Math::BigInt->new(1),
+                Math::BigInt->new(1), Math::BigInt->new(2)];
+
+core();
+
+
+
+sub pdv_iter {
+    my ($a, $b, $c, $d) = @{$pdvstate};
+    ($a, $b, $c, $d) = ($b, $c, $d, $b+$c);
+    @$pdvstate = ($a, $b, $c, $d);
+    return $c;
+}
+
+
+
+sub core {
+    my $ind = 3;  # the index is set to be consistent with OEIS:A112882
+    while (scalar @ans < $NUM_OF_TERMS) {
+        my $Pk = pdv_iter();
+        if (is_prime($Pk)) {
+            update_ans($Pk);
+        }
+        $ind++;
+    }
+}
+
+
+
+sub update_ans {
+    my $candidate = $_[0];
+    push @ans, $candidate if    defined($ans[-1]) 
+                             && $candidate != $ans[-1];
+    push @ans, $candidate if !defined($ans[-1]);
+    return $ans[-1];
+}
diff --git a/challenge-154/cheok-yin-fung/perl/ch-2.pl b/challenge-154/cheok-yin-fung/perl/ch-2.pl
index 8ebe5d7ae5..9783f4ef4b 100644
--- a/challenge-154/cheok-yin-fung/perl/ch-2.pl
+++ b/challenge-154/cheok-yin-fung/perl/ch-2.pl
@@ -6,8 +6,8 @@ use v5.22.0;
 use warnings;
 use Math::BigInt;
 
-use Math::Prime::Util ':all';
-prime_precalc(10_000_000);
+use Math::Prime::Util qw/prime_precalc is_prime/;
+prime_precalc(100_000_000);
 
 
 
@@ -34,7 +34,7 @@ sub core {
     my $ind = 3;  # the index is set to be consistent with OEIS:A112882
     while (scalar @ans < $NUM_OF_TERMS) {
         my $Pk = pdv_iter();
-        if (is_prob_prime($Pk)) {
+        if (is_prime($Pk)) {
             say update_ans($Pk);
         }
         $ind++;