1 files changed, 83 insertions, 0 deletions
diff --git a/challenge-088/ulrich-rieke/perl/ch-2.pl b/challenge-088/ulrich-rieke/perl/ch-2.pl
index 46790eaba6..efe7d005f7 100644
--- a/challenge-088/ulrich-rieke/perl/ch-2.pl
+++ b/challenge-088/ulrich-rieke/perl/ch-2.pl
@@ -29,3 +29,86 @@ sub enterArray {
   }
   return @array ;
 }
+
+#find the direction of the next move across the array, depending on
+#which row and which column we are at and on the information whether
+#we were there already. This info is contained in the $visited array
+#then, in the main program, we call this function for every field and
+#thus determine the next move
+sub findDirection {
+  my ($visited, $currentRow , $currentCol , $direction ) = @_ ;
+  state $maxrows = scalar @$visited ;
+  state $maxcols = length $visited->[0] ;
+  if ( $direction eq "right" ) {
+      if ( $currentCol + 1 < $maxcols and
+        substr( $visited->[$currentRow], $currentCol + 1 , 1 ) eq 'n' ) {
+    $direction = "right" ;
+      }
+      else {
+    $direction = "down" ;
+      }
+    }
+    if ( $direction eq "down" ) {
+    if ( $currentRow + 1 < $maxrows and
+          substr( $visited->[$currentRow + 1], $currentCol , 1 ) eq 'n' ) {
+        $direction = "down" ;
+    }
+    else {
+        $direction = "left" ;
+    }
+    }
+    if ( $direction eq "left" ) {
+    if ( $currentCol - 1 > -1 and
+          substr( $visited->[$currentRow], $currentCol - 1 , 1 ) eq 'n' ) {
+        $direction = "left" ;
+    }
+    else {
+        $direction = "up" ;
+    }
+    }
+    if ( $direction eq "up" ) {
+    if ( $currentRow - 1 > -1  and
+          substr( $visited->[$currentRow - 1], $currentCol  , 1 ) eq 'n' ) {
+        $direction = "up" ;
+    }
+    else {
+        $direction = "right" ;
+    }
+    }
+    return $direction ;
+}
+
+my $m = $ARGV[ 0 ] ;
+my $n = $ARGV[ 1 ] ;
+my @fields_seen ; #Were we here already ? initiated with 'n' for no
+my $unvisitedRow = 'n' x $n ;
+for ( 0 .. $m - 1 ) {
+  push @fields_seen, $unvisitedRow ;
+}
+my $curRow = 0 ;
+my $curCol = 0 ;
+my @array = enterArray( $m , $n ) ;
+my @list ; #holds the numbers in spiral order
+push @list , $array[ 0 ]->[0] ; #we start at the left upper corner
+substr( $fields_seen[ 0 ] , 0 , 1 ) = 'y' ; #and mark this field as seen
+my $dir = "right" ;
+while ( scalar @list < $m * $n ) {#find the direction and move accordingly
+  $dir = findDirection(\@fields_seen, $curRow , $curCol , $dir ) ;
+  if ( $dir eq "right" ) {
+      $curCol++ ;
+  }
+  if ( $dir eq "left" ) {
+      $curCol-- ;
+  }
+  if ( $dir eq "up" ) {
+      $curRow-- ;
+  }
+  if ( $dir eq "down" ) {
+      $curRow++ ;
+  }
+  substr( $fields_seen[$curRow] , $curCol , 1 ) = 'y' ;#mark as seen
+  push @list , $array[ $curRow ]->[ $curCol ] ;#and add to the spiral list
+}
+print "[ " ;
+map { print "$_ " } split ( // , join (',' , @list ) ) ;
+print " ]\n" ;