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Task/N-queens-problem/Arc/n-queens-problem.arc

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+(def nqueens (n (o queens))
+  (if (< len.queens n)
+    (let row (if queens (+ 1 queens.0.0) 0)
+      (each col (range 0 (- n 1))
+        (let new-queens (cons (list row col) queens)
+          (if (no conflicts.new-queens)
+            (nqueens n new-queens)))))
+    (prn queens)))
+
+; check if the first queen in 'queens' lies on the same column or diagonal as
+; any of the others
+(def conflicts (queens)
+  (let (curr . rest) queens
+    (or (let curr-column curr.1
+          (some curr-column (map [_ 1] rest)))  ; columns
+        (some [diagonal-match curr _] rest))))
+
+(def diagonal-match (curr other)
+  (is (abs (- curr.0 other.0))
+      (abs (- curr.1 other.1))))