- Added solutions by Michael Hamlin.

5 files changed, 166 insertions, 0 deletions

diff --git a/challenge-015/michael-hamlin/README b/challenge-015/michael-hamlin/README
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+Solutions by Michael Hamlin.
diff --git a/challenge-015/michael-hamlin/perl5/GetPrime.pm b/challenge-015/michael-hamlin/perl5/GetPrime.pm
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+++ b/challenge-015/michael-hamlin/perl5/GetPrime.pm
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+#! /usr/bin/env perl
+
+#  find primes (sort-of) efficiently (without a sieve)
+#  for an exercise without using cpan...
+
+package GetPrime;
+
+use 5.18.0;
+use parent 'Exporter';
+our @EXPORT = qw<getprime>;
+
+use integer;
+
+my @primes = (2, 3, 5);
+sub getprime ($) {
+    my $n = shift || die "must give an ordinal number to getprime";
+    push @primes, _nextprime() while @primes < $n;
+    return $primes[$n - 1];
+}
+
+sub _nextprime {
+    my $n;
+    for ($n = $primes[-1] + 2; _hasfactor($n); $n += 2) { }
+    return $n;
+}
+sub _hasfactor {
+    my ($n) = @_;
+    # dont bother testing when ending in 5...
+    return 5 if $n =~ /5$/;
+    # we only get odds, so we dont need...
+    # return 2 if $n =~ /[02468]$/;
+
+    my $maxfactor = sqrt($n);
+    foreach my $p (@primes) {
+        return $p unless $n % $p;
+        last if $p >= $maxfactor;
+    }
+    return 0;
+}
+
+1;
+
+__END__
+#foreach (1..20) {
+#    printf "%2u: %u\n", $_, getprime($_);
+#}
+say 'the hundredth prime is ', getprime(100);
+
diff --git a/challenge-015/michael-hamlin/perl5/Vignere.pm b/challenge-015/michael-hamlin/perl5/Vignere.pm
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+++ b/challenge-015/michael-hamlin/perl5/Vignere.pm
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+package Vigenere;
+
+# implement the cipher of the same name.
+
+use 5.18.0;
+use parent 'Exporter';
+our @EXPORT = qw<vencode vdecode>;
+
+use integer;
+use List::SomeUtils qw<pairwise>;
+
+my $basis = join '', 'A' .. 'Z';
+my $blength = length $basis;
+
+our $debug = 0;
+
+sub _normalize {
+    return unless my $plaintext = uc(shift);
+    $plaintext =~ tr/A-Z//cd;
+    return $plaintext;
+}
+sub _ordify {
+    return map {ord($_) - 65} split //, shift;
+}
+sub _stringify {
+    return join '', map {chr($_ + 65)} @_;
+}
+sub _keyshifts {
+    my ($key, $len) = @_;
+    my @rots = _ordify($key);
+    push @rots, @rots while @rots < $len;
+    splice(@rots, $len);
+    return @rots;
+}
+
+
+sub vencode ($@) {
+    my $msg = _normalize(shift) || die "cipher can only encode ascii letters";
+    while (my $key = _normalize(shift)) {
+        say "key:  [$key]" if $debug;
+        my @mchars = _ordify($msg);
+        my @rots = _keyshifts($key, length($msg));
+        my @res = pairwise {($a + $b) % $blength} @mchars, @rots;
+        $msg = _stringify(@res);
+        if ($debug) {
+            say "msg @mchars";
+            say "rot @rots";
+            say "res @res";
+        }
+    }
+    return $msg;
+}
+
+sub vdecode ($@) {
+    my $msg = shift;
+    die "some chars in ciphertext cannot have been encoded" if $msg =~ tr/A-Z/ /c;
+    while (my $key = _normalize(shift)) {
+        my @mchars = _ordify($msg);
+        my @rots = _keyshifts($key, length($msg));
+        my @res = pairwise {($blength + $a - $b) % $blength} @mchars, @rots;
+        $msg = _stringify(@res);
+    }
+    return $msg;
+}
+1;
+
diff --git a/challenge-015/michael-hamlin/perl5/ch-1.pl b/challenge-015/michael-hamlin/perl5/ch-1.pl
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index 0000000000..bbbf14099c
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+++ b/challenge-015/michael-hamlin/perl5/ch-1.pl
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+#! /usr/bin/env perl
+
+use 5.18.0;
+use GetPrime;
+use integer;
+
+my $n = shift @ARGV || 10;
+
+my (@strong, @weak);
+
+for (my $i = 2; @strong < $n && @weak < $n; $i++) {
+    my $prime = getprime($i);
+    # avoiding division for speed
+
+    my $doubled = 2 * $prime;  # saves an op later
+    my $neighbor_sum = getprime($i-1) + getprime($i+1);
+
+    if ($doubled > $neighbor_sum) {
+        push @strong, $prime;
+    } elsif ($doubled < $neighbor_sum) {
+        push @weak, $prime;
+    } else {
+        say "zomg prime #$i ($prime) is neither!"
+}
+}
+
+say "Strongs are: @strong";
+say "Weaks are: @weak";
diff --git a/challenge-015/michael-hamlin/perl5/ch-2.pl b/challenge-015/michael-hamlin/perl5/ch-2.pl
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index 0000000000..9d30e5e5a1
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+++ b/challenge-015/michael-hamlin/perl5/ch-2.pl
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+#! /usr/bin/env perl
+
+use 5.18.0;
+use Vigenere;
+
+use Getopt::Long;
+
+my %opt;
+GetOptions(\%opt,
+    'key|k=s@',
+    'msg|m=s',
+);
+
+my $plaintext = $opt{msg} || 'attack at dawn';
+my @keys = $opt{key} ? @{ $opt{key} } : 'lemon';
+
+my $cipher  = vencode($plaintext, @keys);
+my $decoded = vdecode($cipher, reverse @key
+s);
+
+print "ciphertext: $cipher\n";
+print "decoded:    $decoded\n";
+