NQueens

scala/src/main/scala/ch39_back_tracking/NQueens.scala

@@ -0,0 +1,77 @@
+package ch39_back_tracking
+
+import scala.util.control.Breaks.{break, breakable}
+
+class NQueens(numberOfQueens:Int) {
+  //use array index to identify the row,the value of the row to identify the column
+  val result = new Array[Int](numberOfQueens)
+  var count = 0
+
+  def calcNQueues(row: Int): Unit = {
+    if (row == numberOfQueens) {
+      //everything is done
+      printNQueens()
+      return
+    }
+
+    for (column <- Range(0, numberOfQueens)) {
+      if (isOkOnColumn(row, column)) {
+        result(row) = column //place the column value into the array
+        calcNQueues(row + 1) //calculate next row
+      }
+    }
+
+  }
+
+  def isOkOnColumn(row: Int, column: Int): Boolean = {
+    var ok = true
+    var leftUp = column - 1
+    var rightUp = column + 1
+
+    breakable {
+      //will compare all the rows above current row
+      for (i <- row - 1 to 0 by -1) {
+        //check current column
+        if (result(i) == column) {
+          ok = false
+          break
+        }
+        //check left up
+        if (leftUp >= 0) {
+          if (result(i) == leftUp) {
+            ok = false
+            break
+          }
+        }
+        //check right up
+        if (rightUp < numberOfQueens) {
+          if (result(i) == rightUp) {
+            ok = false
+            break
+          }
+        }
+        //move leftUp and rightUp
+        leftUp -= 1
+        rightUp += 1
+      }
+    }
+
+    ok
+  }
+
+  def printNQueens(): Unit = {
+    count +=1
+    for (row <- Range(0, numberOfQueens)) {
+      for (column <- Range(0, numberOfQueens)) {
+        if (result(row) == column) {
+          print("Q ")
+        } else {
+          print("* ")
+        }
+      }
+      //new line for next row
+      println("")
+    }
+    println(count+"==============")
+  }
+}

scala/src/test/scala/ch39_back_tracking/NQueensTest.scala

@@ -0,0 +1,21 @@
+package ch39_back_tracking
+
+import org.scalatest.FlatSpec
+
+class NQueensTest extends FlatSpec {
+
+  behavior of "NQueensTest"
+
+  it should "calc8Queues" in {
+    val eightQueens = new NQueens(8)
+    eightQueens.calcNQueues(0)
+
+  }
+
+  it should "calc4Queues" in {
+    val eightQueens = new NQueens(4)
+    eightQueens.calcNQueues(0)
+
+  }
+
+}