Just another update

Task/N-queens-problem/SQL/n-queens-problem.sql

@@ -0,0 +1,29 @@
+WITH RECURSIVE
+  positions(i) as (
+    VALUES(0)
+    UNION SELECT ALL
+    i+1 FROM positions WHERE i < 63
+    ),
+  solutions(board, n_queens) AS (
+    SELECT '----------------------------------------------------------------', cast(0 AS bigint)
+      FROM positions
+    UNION
+    SELECT
+      substr(board, 1, i) || '*' || substr(board, i+2),n_queens + 1 as n_queens
+      FROM positions AS ps, solutions
+    WHERE n_queens < 8
+      AND substr(board,1,i) != '*'
+      AND NOT EXISTS (
+        SELECT 1 FROM positions WHERE
+          substr(board,i+1,1) = '*' AND
+            (
+                i % 8 = ps.i %8 OR
+                cast(i / 8 AS INT) = cast(ps.i / 8 AS INT) OR
+                cast(i / 8 AS INT) + (i % 8) = cast(ps.i / 8 AS INT) + (ps.i % 8) OR
+                cast(i / 8 AS INT) - (i % 8) = cast(ps.i / 8 AS INT) - (ps.i % 8)
+            )
+        LIMIT 1
+        )
+   ORDER BY n_queens DESC -- remove this when using Postgres (they don't support ORDER BY in CTEs)
+  )
+SELECT board,n_queens FROM solutions WHERE n_queens = 8;