added assignment 6 ex 4

src/Assignment6/Ex4.sc

@@ -0,0 +1,39 @@
+def inCheck(q1: (Int, Int), q2: (Int, Int)) =
+    q1._1 == q2._1 || // same row
+    q1._2 == q2._2 || // same column
+    (q1._1 - q2._1).abs == (q1._2 - q2._2).abs // on diagonal
+
+def isSafe(queen: (Int, Int), queens: List[(Int, Int)]) =
+    queens forall (q => !inCheck(queen, q))
+
+def queens(n: Int): List[List[(Int, Int)]] = {
+    def placeQueens(k: Int): List[List[(Int, Int)]] =
+        if (k == 0)
+            List(List())
+        else
+            for {
+                queens <- placeQueens(k - 1)
+                column <- 1 to n
+                queen = (k, column)
+                if isSafe(queen, queens)
+            } yield queen :: queens
+
+    placeQueens(n)
+}
+
+def printChessBoard(solutions: List[List[(Int, Int)]]): String = {
+  val sols: List[String] = for ((sol, i) <- solutions.zipWithIndex) yield {
+    val lines: IndexedSeq[String] = for (y <- 1 to sol.length) yield {
+      val line: IndexedSeq[String] = {
+        for (x <- 1 to sol.length) yield {
+          if (sol contains (y, x)) "♕" else "_"
+        }
+      }
+      line.mkString("|", "|", "|")
+    }
+    s"Solution $i:\n" + lines.mkString("\n")
+  }
+  sols.mkString("\n\n")
+}
+
+println(printChessBoard(queens(4)))