Update ch-2.pl

This is adding in a new way of solving the problem...

1 files changed, 45 insertions, 0 deletions

diff --git a/challenge-089/james-smith/perl/ch-2.pl b/challenge-089/james-smith/perl/ch-2.pl
index 25befeef39..b9c086b9bb 100644
--- a/challenge-089/james-smith/perl/ch-2.pl
+++ b/challenge-089/james-smith/perl/ch-2.pl
@@ -32,3 +32,48 @@ sub magic {
   }
   return @solutions;
 }
+
+### Now the bit below is another solution....
+
+## This looks at all the rules and applies them sequentially
+## You need to follow upwards
+
+## We can generate all values if we only have a, b & e
+## If we do this we get the sums of the 2nd and 3rd row as 3e & 30-3e respectively
+## For these to both be 15 e must be 5.
+
+## As e is 5 we only have to loop over a - $a and b - $_.
+
+print
+  ## Render output...
+  map {
+    map(
+      { "  [ @{$_} ]\n" }
+      @{$_}
+    ),
+    "\n"
+  }
+  ## Get magic square....
+  map {
+    $a = $_;
+    ## Return square...
+    map  { [
+      [    $a          ,  $_     ,  -$a - $_ + 15 ],
+      [ -2*$a - $_ + 20,        5, 2*$a + $_ - 10 ],
+      [    $a + $_ -  5, -$_ + 10,  -$a +      10 ]
+    ] }
+    ## Now we filter a/b...
+    grep { 20 >  2*$a +   $_ }      # f is a single digit
+    grep { 10 <  2*$a +   $_ }      # ------- " ---------
+    grep { 25 != 3*$a + 2*$_ }      # a != f ( f = 2a - b - 10 )
+    grep { 20 != 3*$a +   $_ }      # a != d ( d = 20 - 2a - b )
+    grep { 15 !=   $a + 2*$_ }      # c != b
+    grep { 15 != 2*$a +   $_ }      # c != a ( c = 15 - a - b )
+    grep { 10 !=   $a +   $_ }      # c != e ( 5 )
+    grep { 0  !=  -$a +   $_ }      # a != b
+    grep { 5  !=          $_ }      # b != e ( 5 )
+    $a < 6 ? 6-$a .. 9 : 1 .. 14-$a # ensure c is a single digit number
+  }
+  1..4 , 6..9;                      # a != e ( 5 )
+
+