Java Program to Implement ScapeGoat Tree

This is a Java Program to implement ScapeGoat Tree. A scapegoat tree is a self-balancing binary search tree which provides worst-case O(log n) lookup time, and O(log n) amortized insertion and deletion time.

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

/*
 * Java Program to Implement ScapeGoat Tree
 */
 
import java.util.Scanner;    
 
/* Class SGTNode */
class SGTNode    
{
    SGTNode right, left, parent;
    int value;
 
    /* Constructor */
    public SGTNode(int val)
    {
        value = val;
    }
}
 
/* Class ScapeGoatTree */
class ScapeGoatTree
{
    private SGTNode root;
    private int n, q;
 
    /* Constructor */    
    public ScapeGoatTree()
    {
        root = null;
        // size = 0
        n = 0;        
    }
    /* Function to check if tree is empty */
    public boolean isEmpty()
    {
        return root == null;
    }
    /* Function to clear  tree */
    public void makeEmpty()
    {
        root = null;
        n = 0;
    }    
    /* Function to count number of nodes recursively */
    private int size(SGTNode r)
    {
        if (r == null)
            return 0;
        else
        {
            int l = 1;
            l += size(r.left);
            l += size(r.right);
            return l;
        }
    }
    /* Functions to search for an element */
    public boolean search(int val)
    {
        return search(root, val);
    }
    /* Function to search for an element recursively */
    private boolean search(SGTNode r, int val)
    {
        boolean found = false;
        while ((r != null) && !found)
        {
            int rval = r.value;
            if (val < rval)
                r = r.left;
            else if (val > rval)
                r = r.right;
            else
            {
                found = true;
                break;
            }
            found = search(r, val);
        }
        return found;
    }
    /* Function to return current size of tree */   
    public int size() 
    {
        return n;
    }
    /* Function for inorder traversal */
    public void inorder()
    {
        inorder(root);
    }
    private void inorder(SGTNode r)
    {
        if (r != null)
        {
            inorder(r.left);
            System.out.print(r.value +" ");
            inorder(r.right);
        }
    }
    /* Function for preorder traversal */
    public void preorder()
    {
        preorder(root);
    }
    private void preorder(SGTNode r)
    {
        if (r != null)
        {
            System.out.print(r.value +" ");
            preorder(r.left);             
            preorder(r.right);
        }
    }
    /* Function for postorder traversal */
    public void postorder()
    {
        postorder(root);
    }
    private void postorder(SGTNode r)
    {
        if (r != null)
        {
            postorder(r.left);             
            postorder(r.right);
            System.out.print(r.value +" ");
        }
    }     
    private static final int log32(int q) 
    {
        final double log23 = 2.4663034623764317;
        return (int)Math.ceil(log23*Math.log(q));
    }
    /* Function to insert an element */
    public boolean add(int x) 
    {
        /* first do basic insertion keeping track of depth */
        SGTNode u = new SGTNode(x);
        int d = addWithDepth(u);
        if (d > log32(q)) {
            /* depth exceeded, find scapegoat */
            SGTNode w = u.parent;
            while (3*size(w) <= 2*size(w.parent))
                w = w.parent;
            rebuild(w.parent);
        }
        return d >= 0;
    }
    /* Function to rebuild tree from node u */
    protected void rebuild(SGTNode u) 
    {
        int ns = size(u);
        SGTNode p = u.parent;
        SGTNode[] a = new SGTNode[ns];
        packIntoArray(u, a, 0);
        if (p == null) 
        {
            root = buildBalanced(a, 0, ns);
            root.parent = null;
        } 
        else if (p.right == u) 
        {
            p.right = buildBalanced(a, 0, ns);
            p.right.parent = p;
        } 
        else 
        {
            p.left = buildBalanced(a, 0, ns);
            p.left.parent = p;
        }
    }
    /* Function to packIntoArray */
    protected int packIntoArray(SGTNode u, SGTNode[] a, int i) 
    {
        if (u == null) 
        {
            return i;
        }
        i = packIntoArray(u.left, a, i);
        a[i++] = u;
        return packIntoArray(u.right, a, i);
    }
    /* Function to build balanced nodes */
    protected SGTNode buildBalanced(SGTNode[] a, int i, int ns) 
    {
        if (ns == 0)
            return null;
        int m = ns / 2;
        a[i + m].left = buildBalanced(a, i, m);
        if (a[i + m].left != null)
            a[i + m].left.parent = a[i + m];
        a[i + m].right = buildBalanced(a, i + m + 1, ns - m - 1);
        if (a[i + m].right != null)
            a[i + m].right.parent = a[i + m];
        return a[i + m];
    }
    /* Function add with depth */
    public int addWithDepth(SGTNode u) 
    {
        SGTNode w = root;
        if (w == null) 
        {
            root = u;
            n++; 
            q++;
            return 0;
        }
        boolean done = false;
        int d = 0;
        do {
 
            if (u.value < w.value) 
            {
                if (w.left == null) 
                {
                    w.left = u;
                    u.parent = w;
                    done = true;
                } 
                else 
                {
                    w = w.left;
                }
            } 
            else if (u.value > w.value) 
            {
                if (w.right == null) 
                {
                    w.right = u;
                    u.parent = w;
                    done = true;
                }
                w = w.right;
            } 
            else 
            {
                return -1;
            }
            d++;
        } while (!done);
        n++; 
        q++;
        return d;
    }
}
 
public class ScapeGoatTreeTest
{
    public static void main(String[] args)
    {                 
        Scanner scan = new Scanner(System.in);
        /* Creating object of ScapeGoatTree */
        ScapeGoatTree sgt = new ScapeGoatTree(); 
        System.out.println("ScapeGoat Tree Test\n");          
        char ch;
        /*  Perform tree operations  */
        do    
        {
            System.out.println("\nScapeGoat Tree Operations\n");
            System.out.println("1. insert ");
            System.out.println("2. count nodes");
            System.out.println("3. search"); 
            System.out.println("4. check empty");
            System.out.println("5. make empty");
 
            int choice = scan.nextInt();            
            switch (choice)
            {
            case 1 : 
                System.out.println("Enter integer element to insert");
                sgt.add( scan.nextInt() );                     
                break;                                                    
            case 2 : 
                System.out.println("Nodes = "+ sgt.size());
                break; 
            case 3 : 
                System.out.println("Enter integer element to search");
                System.out.println("Search result : "+ sgt.search( scan.nextInt() ));
                break;                           
            case 4 :  
                System.out.println("Empty status = "+ sgt.isEmpty());
                break;
            case 5 :  
                System.out.println("\nTree cleared\n");
                sgt.makeEmpty();
                break;             
            default : 
                System.out.println("Wrong Entry \n ");
                break;           
            }
            /*  Display tree  */ 
            System.out.print("\nPost order : ");
            sgt.postorder();
            System.out.print("\nPre order : ");
            sgt.preorder();
            System.out.print("\nIn order : ");
            sgt.inorder();
 
            System.out.println("\nDo you want to continue (Type y or n) \n");
            ch = scan.next().charAt(0);                        
        } while (ch == 'Y'|| ch == 'y');               
    }
}

ScapeGoat Tree Test
 
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
34
 
Post order : 34
Pre order : 34
In order : 34
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
67
 
Post order : 67 34
Pre order : 34 67
In order : 34 67
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
11
 
Post order : 11 67 34
Pre order : 34 11 67
In order : 11 34 67
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
24
 
Post order : 24 11 67 34
Pre order : 34 11 24 67
In order : 11 24 34 67
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
6
 
Post order : 6 24 11 67 34
Pre order : 34 11 6 24 67
In order : 6 11 24 34 67
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
97
 
Post order : 6 24 11 97 67 34
Pre order : 34 11 6 24 67 97
In order : 6 11 24 34 67 97
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
12
 
Post order : 6 12 24 11 97 67 34
Pre order : 34 11 6 24 12 67 97
In order : 6 11 12 24 34 67 97
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
1
Enter integer element to insert
57
 
Post order : 6 12 24 11 57 97 67 34
Pre order : 34 11 6 24 12 67 57 97
In order : 6 11 12 24 34 57 67 97
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
2
Nodes = 8
 
Post order : 6 12 24 11 57 97 67 34
Pre order : 34 11 6 24 12 67 57 97
In order : 6 11 12 24 34 57 67 97
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
3
Enter integer element to search
57
Search result : true
 
Post order : 6 12 24 11 57 97 67 34
Pre order : 34 11 6 24 12 67 57 97
In order : 6 11 12 24 34 57 67 97
Do you want to continue (Type y or n)
 
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
5
 
Tree cleared
 
 
Post order :
Pre order :
In order :
Do you want to continue (Type y or n)
 
y
 
ScapeGoat Tree Operations
 
1. insert
2. count nodes
3. search
4. check empty
5. make empty
4
Empty status = true
 
Post order :
Pre order :
In order :
Do you want to continue (Type y or n)
 
n