chapter 20 Exercise 22 + 21

Author: HarryDulaney

ch_20/exercise20_09/Exercise20_09.java renamed to ch_20/Exercise20_09.java

@@ -1,4 +1,4 @@
-package ch_20.exercise20_09;
+package ch_20;
 
 
 import javafx.animation.KeyFrame;

ch_20/exercise20_18/Exercise20_18.java renamed to ch_20/Exercise20_18.java

@@ -1,4 +1,4 @@
-package ch_20.exercise20_18;
+package ch_20;
 
 import java.io.File;
 

ch_20/Exercise20_21.java

@@ -25,7 +25,7 @@ public static void main(String[] args) {
 
         selectionSort(list, new GeometricObjectComparator());
         for (int i = 0; i < list.length; i++) {
-            System.out.println("Area of GeometricObject: list[" + i + "] = " + list[i].getArea());
+            System.out.println("Area of GeometricObject @ list[" + i + "] = " + list[i].getArea());
         }
     }
 

ch_20/Exercise20_22.java

@@ -0,0 +1,63 @@
+package ch_20;
+
+import java.util.Scanner;
+import java.util.Stack;
+
+/**
+ * 20.22 (Nonrecursive Tower of Hanoi) Implement the moveDisks method in Listing
+ * 18.8 using a stack instead of using recursion.
+ */
+public class Exercise20_22 {
+
+    private static final Stack<HanoiMove> STACK = new java.util.Stack<>();
+
+    public static void main(String[] args) {
+
+        Scanner input = new Scanner(System.in);
+        System.out.print("Enter number of disks: ");
+        int n = input.nextInt();
+        System.out.println("The moves are:");
+        moveDisks(n, 'A', 'B', 'C');
+    }
+
+    public static void moveDisks(int n, char fromTower,
+                                 char toTower, char auxTower) {
+        STACK.push(new HanoiMove(false, n, fromTower, toTower, auxTower));
+        while (!STACK.isEmpty()) {
+            HanoiMove hanoiMove = STACK.pop();
+            n = hanoiMove.n;
+            fromTower = hanoiMove.fromTower;
+            toTower = hanoiMove.toTower;
+            auxTower = hanoiMove.auxTower;
+            if (hanoiMove.isLastInFromTower)
+                System.out.println("Move disk " + n + " from " +
+                        hanoiMove.fromTower + " to " + hanoiMove.toTower);
+            else {
+                if (n == 1)
+                    System.out.println("Move disk " + n + " from " +
+                            hanoiMove.fromTower + " to " + hanoiMove.toTower);
+                else {
+                    STACK.push(new HanoiMove(false, n - 1, auxTower, toTower, fromTower));
+                    STACK.push(new HanoiMove(true, n, fromTower, toTower, auxTower));
+                    STACK.push(new HanoiMove(false, n - 1, fromTower, auxTower, toTower));
+                }
+            }
+        }
+    }
+
+    public static class HanoiMove {
+        boolean isLastInFromTower = false;
+        int n;
+        char fromTower;
+        char toTower;
+        char auxTower;
+
+        HanoiMove(boolean isLastInFromTower, int n, char fromTower, char toTower, char auxTower) {
+            this.isLastInFromTower = isLastInFromTower;
+            this.n = n;
+            this.fromTower = fromTower;
+            this.toTower = toTower;
+            this.auxTower = auxTower;
+        }
+    }
+}