Data commit

Task/N-queens-problem/Scala/n-queens-problem.scala

@@ -0,0 +1,49 @@
+object NQueens {
+
+  private implicit class RichPair[T](
+    pair: (T,T))(
+    implicit num: Numeric[T]
+  ) {
+    import num._
+
+    def safe(x: T, y: T): Boolean =
+      pair._1 - pair._2 != abs(x - y)
+  }
+
+  def solve(n: Int): Iterator[Seq[Int]] = {
+    (0 to n-1)
+      .permutations
+      .filter { v =>
+        (0 to n-1).forall { y =>
+          (y+1 to n-1).forall { x =>
+            (x,y).safe(v(x),v(y))
+          }
+        }
+      }
+  }
+
+  def main(args: Array[String]): Unit = {
+    val n = args.headOption.getOrElse("8").toInt
+    val (solns1, solns2) = solve(n).duplicate
+    solns1
+      .zipWithIndex
+      .foreach { case (soln, i) =>
+        Console.out.println(s"Solution #${i+1}")
+        output(n)(soln)
+      }
+    val n_solns = solns2.size
+    if (n_solns == 1) {
+      Console.out.println("Found 1 solution")
+    } else {
+      Console.out.println(s"Found $n_solns solutions")
+    }
+  }
+
+  def output(n: Int)(board: Seq[Int]): Unit = {
+    board.foreach { queen =>
+      val row =
+        "_|" * queen + "Q" + "|_" * (n-queen-1)
+      Console.out.println(row)
+    }
+  }
+}