Subversion Repositories programming

// Written by Ira Snyder
// Due Date: 11-24-2004
// Project #4

import java.io.*;
import java.util.*;

class AVLTree {
    private int key, height;
    private AVLTree left, right;

    public static final AVLTree NIL = new AVLTree();

    public AVLTree( int key ) {
        this.key = key;
        left = right = NIL;
    }

    public boolean add( int key ) {
        int oldSize = size();
        grow(key);
        return size() > oldSize;
    }

    public AVLTree grow( int key ) {
        if( this == NIL ) return new AVLTree(key);
        if( key == this.key ) return this; //prevent key dupes
        if( key < this.key ) left = left.grow(key);
        else right = right.grow(key);

        rebalance();

        height = 1 + Math.max(left.height,right.height);
        return this;
    }
    
    public int size() {
        if( this == NIL ) return 0;
        return 1 + left.size() + right.size();
    }

    public String toString() {
        if( this == NIL ) return "";
        return left + " " + key + " " + right;
    }

    private AVLTree() { //construct the empty tree
        left = right = this;
        height = -1;
    }

    private AVLTree( int key, AVLTree left, AVLTree right ) {
        this.key = key;
        this.left = left;
        this.right = right;
        height = 1 + Math.max(left.height,right.height);
    }

    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();
        }
    }

    private void rotateLeft() {
        left = new AVLTree(key,left,right.left);
        key = right.key;
        right = right.right;
    }

    private void rotateRight() {
        right = new AVLTree(key,left.right,right);
        key = left.key;
        left = left.left;
    }
    
} //end AVLTree class