Added the queens perl scripts and a gitignore

2 files changed, 71 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1377554
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.swp
diff --git a/Perl/queens.pl b/Perl/queens.pl
new file mode 100644
index 0000000..81055b9
--- /dev/null
+++ b/Perl/queens.pl
@@ -0,0 +1,70 @@
+#!/usr/bin/perl
+#!/data/data/com.termux/files/usr/bin/perl
+
+if (grep(/^$ARGV[0]$/, ('h', '-h', '--help'))) {
+    print "queens.pl BOARD_SIZE EMPTY_CHAR QUEEN_CHAR\n";
+    exit;
+}
+
+($board_size, $empty, $queen) = (shift // 8, shift // '.', shift // 'Q');
+(@board, $solutions);
+
+place_queen();
+
+sub place_queen {
+    my $row = shift // 0;
+
+    if ($row == $board_size) {
+        $solutions++; 
+        print_solution();
+        return;
+    }
+
+    foreach my $col (0 .. $board_size - 1) {
+        if ($board[$row * $board_size + $col] == 0) {
+            mark($row, $col, 1);
+            place_queen($row + 1);
+            mark($row, $col, -1);
+        }
+    }
+}
+
+sub mark($$$) {
+    my ($row, $col, $value) = @_;
+   
+    foreach my $o (0 .. $board_size - 1) {
+        $board[$row * $board_size + $o] += $value; # row
+        $board[$o * $board_size + $col] += $value; # column
+        
+        # diagonals
+        my ($row_above, $row_below) = ($row - $o, $row + $o);
+        my ($col_left , $col_right) = ($col - $o, $col + $o);
+
+        if ($row_above >= 0 && $col_right < $board_size) {
+            $board[$row_above * $board_size + $col_right] += $value; 
+        }
+        if ($row_above >= 0 && $col_left >= 0) {   
+            $board[$row_above * $board_size + $col_left] += $value; 
+        }
+        if ($row_below < $board_size && $col_left >= 0) {
+            $board[$row_below * $board_size + $col_left] += $value; 
+        }
+        if ($row_below < $board_size && $col_right < $board_size) {
+            $board[$row_below * $board_size + $col_right] += $value;     
+        }
+    }
+    $board[$row * $board_size + $col] += $value;
+}
+
+sub print_solution {
+    print "Solution number $solutions:\n";
+
+    foreach my $row (0 .. $board_size - 1) {
+        foreach my $col (0 .. $board_size - 1) {
+            print(($board[$row * $board_size + $col] == 7) ? $queen : $empty); 
+        }
+        print "\n";
+    }
+
+    print "\n";
+}