Merge pull request #1971 from jacoby/master

Challenge #70

2 files changed, 141 insertions, 0 deletions

diff --git a/challenge-070/dave-jacoby/perl/ch-1.pl b/challenge-070/dave-jacoby/perl/ch-1.pl
new file mode 100755
index 0000000000..bdbb916922
--- /dev/null
+++ b/challenge-070/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,65 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say signatures state };
+no warnings qw{ experimental::signatures };
+
+use Carp;
+use Getopt::Long;
+
+# base case is the example;
+my $string = 'perlandroku';
+my $count  = 3;
+my $offset = 4;
+
+GetOptions(
+    'string=s' => \$string,
+    'count=i'  => \$count,
+    'offset=i' => \$offset,
+);
+
+# constraints
+my $n = length $string;
+$n >= 0               || croak 'String too short';
+$count >= 1           || croak 'Swap Count < 1';
+$offset >= 1          || croak 'Offset < 1';
+$count <= $offset     || croak 'Count > Offset';
+$offset + $count < $n || croak 'Offset + Count < length of String';
+
+char_swap( $string, $count, $offset );
+
+sub char_swap ( $string, $count, $offset ) {
+    my $n = length $string;
+    print <<"END";
+Input:
+    S: $string
+    C: $count
+    O: $offset
+
+Character Swapping:
+END
+
+    for my $c ( 1 .. $count ) {
+
+        # the locations within the string
+        my $p1 = ( $c % $n );
+        my $p2 = ( $c + $offset ) % $n;
+
+        # the characters in said positions
+        my $c1 = substr $string, $p1, 1;
+        my $c2 = substr $string, $p2, 1;
+
+        # since we have the characters stored already
+        # we don't need to store one and place the other
+        substr( $string, $p1, 1 ) = $c2;
+        substr( $string, $p2, 1 ) = $c1;
+
+        say qq{    swap $c: $c1 <=> $c2 = $string};
+    }
+    print <<"END";
+
+Output:
+    $string
+END
+}
diff --git a/challenge-070/dave-jacoby/perl/ch-2.pl b/challenge-070/dave-jacoby/perl/ch-2.pl
new file mode 100755
index 0000000000..c8ca8f11ea
--- /dev/null
+++ b/challenge-070/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,76 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say signatures state };
+no warnings qw{ experimental::signatures };
+
+use Carp;
+use Getopt::Long;
+use JSON;
+
+# base case is the example;
+my $n = 2;
+
+GetOptions( 'number=i' => \$n, );
+
+# constraints
+2 <= $n || croak 'N too small';
+$n <= 5 || croak 'M too big';
+
+say qq{n: $n};
+
+grey_code($n);
+
+sub grey_code ( $n ) {
+
+    # I THINK...
+    # a zero-bit grey sequence would be []
+    # for one bit, add '0' to each nothing to the left,
+    #   '1' to each nothing to the right,
+    #    so we get the one-bit grey sequence of [ 0, 1 ]
+    # for a two-bit grey sequence, we do the same, but
+    #   with actual sequences, which become
+    # [ 00 , 01 , 11, 10 ], which, when turned back to
+    # decimal, becomes...
+    my @sequence = ( 0, 1, 3, 2 );
+
+    # conceptually, we need a while, not a do-while, because
+    # the sequence, right now, is a correct two-bit grey sequence
+    if ( $n > 2 ) {
+        for my $i ( 3 .. $n ) {
+            # s1 is sequence converted to binary
+            # s2 is s1 reversed
+            my @s1 = map { dec2bin( $_, $i ) } @sequence;
+            my @s2 = reverse @s1;
+
+            # we append 0 to all entries in s1
+            # and 1 to all the s2 entries
+            @s1 = map { '0' . $_ } @s1;
+            @s2 = map { '1' . $_ } @s2;
+
+            # and then we join the two into one,
+            my @s3 = ( @s1, @s2 );
+            @sequence = map { bin2dec($_) } @s3;
+        }
+    }
+
+    # JSON object here because it makes this function more
+    # "pure"
+    my $json = JSON->new->space_after;
+    say $json->encode( \@sequence );
+}
+
+# not the dec2bin given by the Perl Cookbook, because
+# we need to control the number of bits, because both
+# 00000010 and 010 are 2, but only one behaves correctly
+# when 1 is prepended.
+# By the way, I LOVE sprintf.
+sub dec2bin ( $n, $i = 2 ) {
+    return sprintf "%0${i}b", $n;
+}
+
+# bin2dec as taken from the Perl Cookbook
+sub bin2dec ($bin) {
+    return unpack( "N", pack( "B32", substr( "0" x 32 . $bin, -32 ) ) );
+}