Java Program to Implement Splay Tree

This is a Java Program to implement Splay Tree. A splay tree is a self-adjusting binary search tree with the additional property that recently accessed elements are quick to access again. It performs basic operations such as insertion, look-up and removal in O(log n) amortized time. For many sequences of non-random operations, splay trees perform better than other search trees, even when the specific pattern of the sequence is unknown. The splay tree was invented by Daniel Dominic Sleator and Robert Endre Tarjan in 1985.

Here is the source code of the Java program to implement Splay Tree. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

/**
 *  Java Program to Implement SplayTree
 **/
 
 import java.util.Scanner;
 
 /** Class Node **/
 class SplayNode
 {    
     SplayNode left, right, parent;
     int element;
 
     /** Constructor **/
     public SplayNode()
     {
         this(0, null, null, null);
     }          
     /** Constructor **/
     public SplayNode(int ele)
     {
         this(ele, null, null, null);
     } 
     /** Constructor **/
     public SplayNode(int ele, SplayNode left, SplayNode right, SplayNode parent)
     {
         this.left = left;
         this.right = right;
         this.parent = parent;
         this.element = ele;         
     }    
 }
 
 /** Class SplayTree **/
 class SplayTree
 {
     private SplayNode root;
     private int count = 0;
 
     /** Constructor **/
     public SplayTree()
     {
         root = null;
     }
 
     /** Function to check if tree is empty **/
     public boolean isEmpty()
     {
         return root == null;
     }
 
     /** clear tree **/
     public void clear()
     {
         root = null;
         count = 0;
     }
 
     /** function to insert element */
     public void insert(int ele)
     {
         SplayNode z = root;
         SplayNode p = null;
         while (z != null)
         {
             p = z;
             if (ele > p.element)
                 z = z.right;
             else
                 z = z.left;
         }
         z = new SplayNode();
         z.element = ele;
         z.parent = p;
         if (p == null)
             root = z;
         else if (ele > p.element)
             p.right = z;
         else
             p.left = z;
         Splay(z);
         count++;
     }
     /** rotate **/
     public void makeLeftChildParent(SplayNode c, SplayNode p)
     {
         if ((c == null) || (p == null) || (p.left != c) || (c.parent != p))
             throw new RuntimeException("WRONG");
 
         if (p.parent != null)
         {
             if (p == p.parent.left)
                 p.parent.left = c;
             else 
                 p.parent.right = c;
         }
         if (c.right != null)
             c.right.parent = p;
 
         c.parent = p.parent;
         p.parent = c;
         p.left = c.right;
         c.right = p;
     }
 
     /** rotate **/
     public void makeRightChildParent(SplayNode c, SplayNode p)
     {
         if ((c == null) || (p == null) || (p.right != c) || (c.parent != p))
             throw new RuntimeException("WRONG");
         if (p.parent != null)
         {
             if (p == p.parent.left)
                 p.parent.left = c;
             else
                 p.parent.right = c;
         }
         if (c.left != null)
             c.left.parent = p;
         c.parent = p.parent;
         p.parent = c;
         p.right = c.left;
         c.left = p;
     }
 
     /** function splay **/
     private void Splay(SplayNode x)
     {
         while (x.parent != null)
         {
             SplayNode Parent = x.parent;
             SplayNode GrandParent = Parent.parent;
             if (GrandParent == null)
             {
                 if (x == Parent.left)
                     makeLeftChildParent(x, Parent);
                 else
                     makeRightChildParent(x, Parent);                 
             } 
             else
             {
                 if (x == Parent.left)
                 {
                     if (Parent == GrandParent.left)
                     {
                         makeLeftChildParent(Parent, GrandParent);
                         makeLeftChildParent(x, Parent);
                     }
                     else 
                     {
                         makeLeftChildParent(x, x.parent);
                         makeRightChildParent(x, x.parent);
                     }
                 }
                 else 
                 {
                     if (Parent == GrandParent.left)
                     {
                         makeRightChildParent(x, x.parent);
                         makeLeftChildParent(x, x.parent);
                     } 
                     else 
                     {
                         makeRightChildParent(Parent, GrandParent);
                         makeRightChildParent(x, Parent);
                     }
                 }
             }
         }
         root = x;
     }
 
     /** function to remove element **/
     public void remove(int ele)
     {
         SplayNode node = findNode(ele);
        remove(node);
     }
 
     /** function to remove node **/
     private void remove(SplayNode node)
     {
         if (node == null)
             return;
 
         Splay(node);
         if( (node.left != null) && (node.right !=null))
         { 
             SplayNode min = node.left;
             while(min.right!=null)
                 min = min.right;
 
             min.right = node.right;
             node.right.parent = min;
             node.left.parent = null;
             root = node.left;
         }
         else if (node.right != null)
         {
             node.right.parent = null;
             root = node.right;
         } 
         else if( node.left !=null)
         {
             node.left.parent = null;
             root = node.left;
         }
         else
         {
             root = null;
         }
         node.parent = null;
         node.left = null;
         node.right = null;
         node = null;
         count--;
     }
 
     /** Functions to count number of nodes **/
     public int countNodes()
     {
         return count;
     }
 
     /** Functions to search for an element **/
     public boolean search(int val)
     {
         return findNode(val) != null;
     }
 
     private SplayNode findNode(int ele)
     {
    	 SplayNode PrevNode = null;
         SplayNode z = root;
         while (z != null)
         {
        	 PrevNode = z;
             if (ele > z.element)
                 z = z.right;
             else if (ele < z.element)
                 z = z.left;
             else if(ele == z.element) {
                 Splay(z);
                 return z;
             }
 
         }
         if(PrevNode != null)
         {
             Splay(PrevNode);
             return null;
         }
         return null;
     }
 
     /** Function for inorder traversal **/ 
     public void inorder()
     {
         inorder(root);
     }
     private void inorder(SplayNode r)
     {
         if (r != null)
         {
             inorder(r.left);
             System.out.print(r.element +" ");
             inorder(r.right);
         }
     }
 
     /** Function for preorder traversal **/
     public void preorder()
     {
         preorder(root);
     }
     private void preorder(SplayNode r)
     {
         if (r != null)
         {
             System.out.print(r.element +" ");
             preorder(r.left);             
             preorder(r.right);
         }
     }
 
     /** Function for postorder traversal **/
     public void postorder()
     {
         postorder(root);
     }
     private void postorder(SplayNode r)
     {
         if (r != null)
         {
             postorder(r.left);             
             postorder(r.right);
             System.out.print(r.element +" ");
         }
     }     
 }
 
 /** Class SplayTreeTest **/
 public class SplayTreeTest
 {
    public static void main(String[] args)
    {            
        Scanner scan = new Scanner(System.in);
        /** Creating object of SplayTree **/
        SplayTree spt = new SplayTree(); 
        System.out.println("Splay Tree Test\n");          
        char ch;
        /**  Perform tree operations  **/
        do    
        {
            System.out.println("\nSplay Tree Operations\n");
            System.out.println("1. insert ");
            System.out.println("2. remove ");
            System.out.println("3. search");
            System.out.println("4. count nodes");
            System.out.println("5. check empty");
            System.out.println("6. clear tree");
 
            int choice = scan.nextInt();            
            switch (choice)
            {
            case 1 : 
                System.out.println("Enter integer element to insert");
                spt.insert( scan.nextInt() );                     
                break;
            case 2 : 
                System.out.println("Enter integer element to remove");
                spt.remove( scan.nextInt() );                     
                break;                          
            case 3 : 
                System.out.println("Enter integer element to search");
                System.out.println("Search result : "+ spt.search( scan.nextInt() ));
                break;                                          
            case 4 : 
                System.out.println("Nodes = "+ spt.countNodes());
                break;     
            case 5 : 
                System.out.println("Empty status = "+ spt.isEmpty());
                break;     
            case 6 : 
                System.out.println("\nTree Cleared");
                spt.clear();
                break;        
            default : 
                System.out.println("Wrong Entry \n ");
                break;   
            }
            /**  Display tree  **/
            System.out.print("\nPost order : ");
            spt.postorder();
            System.out.print("\nPre order : ");
            spt.preorder();
            System.out.print("\nIn order : ");
            spt.inorder(); 
 
            System.out.println("\nDo you want to continue (Type y or n) \n");
            ch = scan.next().charAt(0);                        
        } while (ch == 'Y'|| ch == 'y');               
    }
}

Splay Tree Test
 
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
14
 
Post order : 14 
Pre order : 14 
In order : 14 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
28
 
Post order : 14 28 
Pre order : 28 14 
In order : 14 28 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
19
 
Post order : 14 28 19 
Pre order : 19 14 28 
In order : 14 19 28 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
63
 
Post order : 14 19 28 63 
Pre order : 63 28 19 14 
In order : 14 19 28 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
5
 
Post order : 19 14 63 28 5 
Pre order : 5 28 14 19 63 
In order : 5 14 19 28 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
1
Enter integer element to insert
7
 
Post order : 5 19 63 28 14 7 
Pre order : 7 5 14 28 19 63 
In order : 5 7 14 19 28 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
3
Enter integer element to search
24
Search result : false
 
Post order : 5 14 7 63 28 19 
Pre order : 19 7 5 14 28 63 
In order : 5 7 14 19 28 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
2
Enter integer element to remove
28
 
Post order : 5 14 7 63 19 
Pre order : 19 7 5 14 63 
In order : 5 7 14 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
3
Enter integer element to search
28
Search result : false
 
Post order : 5 14 7 19 63 
Pre order : 63 19 7 5 14 
In order : 5 7 14 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
2
Enter integer element to remove
14
 
Post order : 5 19 63 7 
Pre order : 7 5 63 19 
In order : 5 7 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
2
Enter integer element to remove
7
 
Post order : 19 63 5 
Pre order : 5 63 19 
In order : 5 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
4
Nodes = 3
 
Post order : 19 63 5 
Pre order : 5 63 19 
In order : 5 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
5
Empty status = false
 
Post order : 19 63 5 
Pre order : 5 63 19 
In order : 5 19 63 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
6
 
Tree Cleared
 
Post order : 
Pre order : 
In order : 
Do you want to continue (Type y or n) 
 
y
 
Splay Tree Operations
 
1. insert 
2. remove 
3. search
4. count nodes
5. check empty
6. clear tree
5
Empty status = true
 
Post order : 
Pre order : 
In order : 
Do you want to continue (Type y or n) 
 
n