Subversion Repositories programming

// Written by Ira Snyder

// Due Date: 11-24-2004

// Project #4

// Helped and was Helped By: Allen Oliver

// Got information from: 

//     http://www.cs.dartmouth.edu/~chepner/cs15/notes/08_bst.html

// License: Public Domain, except for code which is from the above source.

// License: I am unsure of their license (added 07-11-2005)

import java.io.*;

import java.util.*;

class AVLTree {

    private int key, height;

    private Object data;

    private AVLTree left, right;

    //create an empty tree to be used instead of checking

    //for nulls all over the place

    public static final AVLTree NIL = new AVLTree();

    //constructor for the basic AVLTree

    public AVLTree( int key, Object data ) {

        this.key = key;

        this.data = data;

        left = right = NIL;

    }

    //method to insert a new key-data pair into the tree

    public boolean add( int key, Object data ) {

        int oldSize = size();

        grow(key,data);

        return size() > oldSize;

    }

    //provide name mapping for add

    public boolean insert( int key, Object data ) {

        return add(key,data);

    }

    //method to add an element to a tree

    private AVLTree grow( int key, Object data ) {

        if( this == NIL ) return new AVLTree(key,data);

        //prevent key dupes, update data

        if( key == this.key ) { this.data = data; return this; } 

        if( key < this.key ) left = left.grow(key,data);

        else right = right.grow(key,data);

        rebalance(); //fix the balance as we recurse back up

        height = 1 + Math.max(left.height,right.height);

        return this;

    }

    //method to return the size of the tree

    public int size() {

        if( this == NIL ) return 0;

        return 1 + left.size() + right.size();

    }

    //I like the BinaryTree toString better than the author's toString()

    //so I used it here instead. I left the author's code for completeness.

    /*

    public String toString() {

        if( this == NIL ) return "";

        return left + " " + key + " " + right;

    }

    */

    //method to print the tree as a String

    public String toString() {

        if( this == NIL ) return "()";

        String sLeft = sLeft = left.toString();

        String sRight = sRight = right.toString();

        String answer = new String();

        //assemble the string to return

        answer = "(";

        if( !sLeft.equals("()") ) { answer += sLeft + ","; }

        answer += key;

        if( !sRight.equals("()") ) { answer += "," + sRight; }

        answer += ")";

        //return the assembled string

        return answer;

    }

    //constructor to make the empty tree

    private AVLTree() {

        left = right = this;

        height = -1;

    }

    //constructor to make a new AVLTree given a key-data pair, and left

    //and right subtrees

    private AVLTree( int key, Object data, AVLTree left, AVLTree right ) {

        this.key = key;

        this.data = data;

        this.left = left;

        this.right = right;

        height = 1 + Math.max(left.height,right.height);

    }

    //method to rebalance the tree if it is out of balance, using rotations

    private void rebalance() {

        if( right.height > (left.height + 1) ) {

            if( right.left.height > right.right.height ) right.rotateRight();

            rotateLeft();

        }

        else if( left.height > (right.height + 1) ) {

            if( left.right.height > left.left.height ) left.rotateLeft();

            rotateRight();

        }

    }

    //method to rotate the tree to the left

    private void rotateLeft() {

        left = new AVLTree(key,data,left,right.left);

        key = right.key;

        data = right.data;

        right = right.right;

    }

    //method to rotate the tree to the right

    private void rotateRight() {

        right = new AVLTree(key,data,left.right,right);

        key = left.key;

        data = left.data;

        left = left.left;

    }

    //method to return the height of the tree

    public int getHeight() { return height; }

    //method to return the height of the subtree with the

    //given key

    public int getHeight( int key ) {

        if( this == NIL ) { return -1; }

        if( key == this.key ) { return getHeight(); }

        if( key < this.key ) { return left.getHeight(key); }

        return right.getHeight(key);

    }

    //method to return the left subtree

    public AVLTree getLeft() { 

        if( this == NIL ) { return NIL; }

        return left;

    }

    //method to return the left subtree of the subtree with the

    //given key

    public AVLTree getLeft( int key ) {

        if( this == NIL ) { return null; } //key not in tree

        if( key == this.key ) { return getLeft(); }

        if( key < this.key ) { return left.getLeft(key); }

        return right.getLeft(key);

    }

    //method to return the right subtree

    public AVLTree getRight() {

        if( this == NIL ) { return NIL; }

        return right;

    }

    //method to return the right subtree of the subtree with the

    //given key

    public AVLTree getRight( int key ) {

        if( this == NIL ) { return null; } //key not in tree

        if( key == this.key ) { return getRight(); }

        if( key < this.key ) { return left.getRight(key); }

        return right.getRight(key);

    }

    //method to return the key of the root

    public int getRoot() { return key; }

    //method to return the key of the root

    public int getKey() { return key; }

    //method to return the data of the root

    public Object getData() { return data; }

    //method to see if the tree contains a key

    public boolean contains( int x ) { 

        if( this == NIL ) { return false; }

        if( key == x ) { return true; }

        return left.contains(x) || right.contains(x);

    }

    //return the data associated with a given key

    public Object get( int key ) {

        if( this == NIL ) { return NIL; }

        if( key == this.key ) { return data; }

        if( key < this.key ) { return left.get(key); }

        return right.get(key);

    }

    //check if two trees are equals

    public boolean equals( Object object ) { 

        if( !(object instanceof AVLTree) ) { return false; }

        AVLTree temp = (AVLTree)object; //make it typed

        boolean l=false, r=false;

        //check the left

        if( left == NIL && temp.left == NIL ) l = true;

        else l = left.equals(temp.left);

        //check the right

        if( right == NIL && temp.right == NIL ) r = true;

        else r = right.equals(temp.right);

        return (temp.key == key) && l && r;

    }

    //method to create a new tree from an array of keys,

    //and an array of data

    public AVLTree( int[] keys, Object[] data ) { 

        //this(keys[0],data[0]); //create a new tree

        if( keys.length != data.length ) { throw new IllegalArgumentException(); }

        this.key = keys[0];

        this.data = data[0];

        left = right = NIL;

        //call add() for every element in the array

        for( int i=1; i < keys.length; i++ ) add(keys[i],data[i]);

    }

    //method to remove a key-data pair from the tree

    public boolean remove( int key ) {

        if( !contains(key) ) { return false; }

        removeHelper(this,key);

        if( contains(key) ) { return false; }

        return true;

    }

    //a helper method for remove, which performs the actual recursion

    private AVLTree removeHelper( AVLTree tree, int key ) {

        if( tree == NIL ) { return NIL; }

        else if( key < tree.key ) { tree.left = removeHelper(tree.left,key); }

        else if( key > tree.key ) { tree.right = removeHelper(tree.right,key); }

        else if( tree.left != NIL && tree.right != NIL ) { 

            tree = deleteMinimum(tree.right); 

        }

        else if( tree.left != NIL ) { tree = tree.left; }

        else { tree = tree.right; }

        tree.rebalance(); //rebalance as we recurse back up

        return tree;

    }

    //method to remove the minimum element in a tree

    private AVLTree deleteMinimum( AVLTree tree ) {

        if( tree == NIL ) { return NIL; }

        if( tree.left == NIL && tree.right == NIL ) { return NIL; }

        if( tree.left == NIL ) { 

            return new AVLTree(tree.right.key,tree.right.data,

                               tree.right.left,tree.right.right); 

        }

        return new AVLTree(tree.key,tree.data,deleteMinimum(tree.left),tree.right);

    }

    //method to print a tree InOrder

    public static void printInOrder( AVLTree tree ) {

        Queue queue = new Queue();

        queue.enqueue(tree);

        while( !queue.isEmpty() ) {

            AVLTree temp = (AVLTree)queue.dequeue();

            System.out.print(temp.getKey()+" ");

            if( temp.getLeft() != NIL ) { queue.enqueue(temp.getLeft()); }

            if( temp.getRight() != NIL ) { queue.enqueue(temp.getRight()); }

        }

    }

    //method to print a tree in PreOrder

    public static void printPreOrder( AVLTree tree ) {

        if( tree == NIL ) return;

        System.out.print(tree.getKey()+" ");

        AVLTree.printPreOrder( tree.getLeft() );

        AVLTree.printPreOrder( tree.getRight() );

    }

} //end AVLTree class