changed comments added blog links

3 files changed, 127 insertions, 49 deletions

diff --git a/challenge-097/james-smith/perl/blog.txt b/challenge-097/james-smith/perl/blog.txt
new file mode 100644
index 0000000000..5b18ca0d4b
--- /dev/null
+++ b/challenge-097/james-smith/perl/blog.txt
@@ -0,0 +1 @@
+http://blogs.perl.org/users/james_curtis-smith/2021/01/perl-weekly-challenge-97.html
diff --git a/challenge-097/james-smith/perl/ch-1.pl b/challenge-097/james-smith/perl/ch-1.pl
index d6dfd58a56..c0a6fae0bc 100644
--- a/challenge-097/james-smith/perl/ch-1.pl
+++ b/challenge-097/james-smith/perl/ch-1.pl
@@ -6,12 +6,31 @@ use warnings;
 use feature qw(say);
 use Test::More;
 
-is( caesar('ABCDEFGHIJKLMNOPQRSTUVWXYZ',3), 'XYZABCDEFGHIJKLMNOPQRSTUVW' );
-is( caesar('THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG',3), 'QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD' );
+is( caesar('ABCDEFGHIJKLMNOPQRSTUVWXYZ',3),
+           'XYZABCDEFGHIJKLMNOPQRSTUVW' );
+is( caesar('THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG',3),
+           'QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD' );
 
 done_testing();
 
 sub caesar {
-  return join q(), map { m{[A-Z]} ? chr 65+(ord($_)-65-$_[1])%26 : $_ } split m{}, $_[0];
+  ## Use regex replace
+  ##  r - return value rather than substitute in original string
+  ##  e - evaluate replace rather than use string
+  ##  g - repeat over all characters
+  ##  x - not needed (comments in match) - but looks good!
+
+  return $_[0] =~ s{([A-Z])}{chr 65+(-65-$_[1]+ord$1)%26}regex;
+
+  ## Note about optimization of brackets in the eval function...
+  ##
+  ## 65 is at the front of the chr block as needing the bracket
+  ##   for the %26 - it would be evaluated as the bracket wrapping
+  ##   the parameters for chr ..{chr(...)+65}
+  ##
+  ## -65 is at the start of the bracket - to allow us to not
+  ##   use brackets for the ord - if it was at the beginning
+  ##   you would need ord as it would evaluate ord $1 - 65 .. as
+  ##   ord( $1 - 65 - ...)
 }
 
diff --git a/challenge-097/james-smith/perl/ch-2.pl b/challenge-097/james-smith/perl/ch-2.pl
index 81f89d7e4f..72ed38f422 100644
--- a/challenge-097/james-smith/perl/ch-2.pl
+++ b/challenge-097/james-smith/perl/ch-2.pl
@@ -6,63 +6,121 @@ use warnings;
 use feature qw(say);
 use Test::More;
 
-is( min_flips('101101',3), 0 );
 is( min_flips('101100101',3), 1 );
 is( min_flips('10110111', 4), 2 );
 is( min_flips('100101100',3), 1 );
 is( min_flips('101100100100101',3), 2 );
+is( min_flips('101101',3), 0 );
 is( min_flips('0000000100100011010001010110011110001001101010111100110111101111',4), 32 );
 
 done_testing();
 
+##  As the first problem was a good one for applying "Golfing"
+##  techniques to it - I thought I would play along and try the
+##  second one....
+##  Notes
+##
+##  This was to use this to serve as an example of perl idioms
+##  that other programmers may find it difficult to understand
+##  - and so I tried to put as many of them in relatively short
+##  function.... a discussion thread on the Perl programmers
+##  facebook group.
+##
+##  * One statement functions are a "lovely" perl concept - even if
+##    they can get a bit difficult to read....
+##
+##  * In perl there are special variables which give you information
+##    about the current process, or allow us to alter the
+##    functionality. To avoid creating variables I use these in the
+##    function. If you change these you can change how the code works -
+##    but here we use "local" copies - so that when we return from the
+##    function (block) they revert to their normal values - so we
+##    don't introduce any side-effects of our code
+##
+##    * $/ - normally the input record separator - we will use for
+##           the minimum value
+##
+##    * $\ - normally the output record separator - we will use for
+##           the number of chunks
+##
+##  * @_ - the list of parameters passed to a function - in this case
+##         $_[0] is the string and $_[1] is the block size
+##
+##  * Chained maps - we can simplify the maps by chaining them
+##    together, here we break it down into 5 separate stages -
+##    remember we have to read the code backwards. So we will look
+##    at the separate blocks of code working upwards...
+##
+##    * 0..$\-1 - this returns a list of indices for the substrings
+##
+##    * map { $_*$_[1] } - this converts those indices into start
+##        locations ($_ is the value of the element of variable that
+##        the map function is processing
+##
+##    * map { [ $_, substr$_[0],$_,$_[1] ] } - this grabs the
+##        substring for the nth block - but keeps the start location
+##        as we will need it later... Here we see a map returning an
+##        arrayref - in subsequent requests - $_->[0] is the start
+##        offset of the block and $_->[1] is the property we are
+##        munging in this case the substring.
+##
+##        You have to be careful here as $_[0] and $_->[0] look similar
+##        but are different
+##
+##    * map { [ $_->[0], $_->[1] x $\ ] } - this maps the string we
+##        just have to have the same length as our original string -
+##        by performing a perl "string multiplication" x
+##
+##    * map { [ $_->[0], ( $_[0] ^ $_->[1] ) =~ y/\x01/\x01/ ] } -
+##        count the flips. Two perlisms here - we can use xor operator
+##        ^ on strings to xor the binary values of each string.
+##        y/../../ - the translate operator returns the number of
+##        substitutions it makes - in this case we are substituting
+##        the ASCII character with decimal a hex value of "01"... when
+##        the strings are same the byte value of the xor is 0 or "\x00"
+##        and when they are different the value is 1 or "\x01"
+##
+##    * map { $/ = !$_->[0] || $_->[1] < $/ ? $_->[1] : $/ } - finally
+##        we keep the running total of the minimum value - Now this is
+##        why we kept the start of the block around - as the first
+##        time through the loop we have to define the minimum - if
+##        $_->[0] is zero then we assign $_->[1] to $/ - we could have
+##        used the List::Util function min - but I try and avoid using
+##        external modules if I can...
+##
+##  * The list is the running minimums so we have to get the last
+##    element off the list - we do this with by wrapping the list
+##    in [ ] to make it an arrayref and then taking its last value
+##    [{list}]->[-1] perl indexes the last element as -1.
+##
+##  * And we return this value.
+
 sub min_flips {
   ## Golf mode on...
-  ##
-  ## This was to use this to serve as an example of perl idioms that other programmers
-  ## may find it difficult to understand - and so I tried to put as many of them in relatively
-  ## short function....
-  ##
-  ## One statement functions are a lovely perl concept - even if they can get a bit difficult
-  ## to read....
-  ##
+  return[
+    local$/,
+    local$\=length($_[0])/$_[1],
+    map{$/=!$_->[0]||$_->[1]<$/?$_->[1]:$/}
+    map{[$_->[0],($_[0]^$_->[1])=~y/\x01/\x01/]}
+    map{[$_->[0],$_->[1]x$\]}
+    map{[$_,substr$_[0],$_,$_[1]]}
+    map{$_*$_[1]}
+    0..$\-1
+  ]->[-1];
+}
+
+## With the white space back in..
 
-  local $/;
+sub min_flips_more_readable {
   return [
-    map {
-      local $\ = ( $_[0] ^ (substr$_[0],$_,$_[1]) x (length($_[0])/$_[1]) ) =~ tr/\x01/\x01/,
-      $/ = (!$_ || ($\ < $/)) ? $\ : $/
-    }
-    map { $_*$_[1] }
-    0 .. ( length($_[0])/$_[1] - 1 )
+    local $/,
+    local $\= length($_[0]) / $_[1],
+
+    map { $/ = !$_->[0] || $_->[1] < $/ ? $_->[1] : $/     }
+    map { [ $_->[0], ( $_[0] ^ $_->[1] ) =~ y/\x01/\x01/ ] }
+    map { [ $_->[0], $_->[1] x $\                        ] }
+    map { [ $_,      substr $_[0], $_, $_[1]             ] }
+    map { $_ * $_[1]                                       }
+    0 .. $\ - 1
   ]->[-1];
-  ## We could use variales here - but playing with localised special variables is fun!
-  ## $/ <- minimum value
-  ## $\ <- value for given chunk....
-  ##
-  ## The inner map + range combination returns a list of ids of the form 0, $n, 2*$n until the
-  ## end of the array, we use this to chunk the array up for comparison
-  ##
-  ## Inside the end map - we first string "xor" the string with the repeated chunk of the array.
-  ## so e.g. for the first example this becomes:
-  ##   '101100101' ^ '101'.'101'.'101'
-  ##   '101100101' ^ '100'.'100'.'100'
-  ##   '101100101' ^ '101'.'101'.'101'
-  ## if the symbols match you get a value \x00, when they don't match you get value \x01
-  ## so we then count the \x01's using tr... and store in $\
-  ##
-  ## Next if it is the first chunk OR the value of $\ is less than the current min ($/)
-  ## We set $/ to $\ otherwise we leave it as $/
-  ##
-  ## The resulting array consists of the value for the node and the running minimum in the examples
-  ##
-  ## for ex 1: it is [0,0,0,0]
-  ## for ex 2: it is [1,1,2,1,1,1]
-  ## for ex 3: it is [1,1,1,1]
-  ## for ex 4: it is [2,2,2,2]
-  ## for ex 5: it is [2,2,1,1,1,1]
-  ##
-  ## We need the last value of this so we wrap the list into an array ref and take the last element
-  ##
-  ## [ list... ]->[-1];
 }
-