java - 红黑树可比

Question

我试图理解下面构建红黑树的代码。

封装模块；

     import java.util.Comparator;
   // RedBlackTree class
//
// CONSTRUCTION: with a negative infinity sentinel
//
// ******************PUBLIC OPERATIONS*********************
// void insert( x )       --> Insert x
// void remove( x )       --> Remove x (unimplemented)
// Comparable find( x )   --> Return item that matches x
// Comparable findMin( )  --> Return smallest item
// Comparable findMax( )  --> Return largest item
// boolean isEmpty( )     --> Return true if empty; else false
// void makeEmpty( )      --> Remove all items
// void printTree( )      --> Print tree in sorted order

/**
 * Implements a red-black tree.
 * Note that all "matching" is based on the compareTo method.
 * @author Mark Allen Weiss
 */
public class RedBlackTree
{
    /**
     * Construct the tree.
     * @param negInf a value less than or equal to all others.
     */
    public RedBlackTree( Comparable negInf )
    {
        header      = new RedBlackNode( negInf );
        header.left = header.right = nullNode;
    }

    /**
     * Insert into the tree. Does nothing if item already present.
     * @param item the item to insert.
     */
    public void insert( Comparable item )
    {
        current = parent = grand = header;
        nullNode.element = item;

        while( current.element.compareTo( item ) != 0 )
        {
            great = grand; grand = parent; parent = current;
            current = item.compareTo( current.element ) < 0 ?
                         current.left : current.right;

                // Check if two red children; fix if so
            if( current.left.color == RED && current.right.color == RED )
                 handleReorient( item );
        }

            // Insertion fails if already present
        if( current != nullNode )
            return;
        current = new RedBlackNode( item, nullNode, nullNode );

            // Attach to parent
        if( item.compareTo( parent.element ) < 0 )
            parent.left = current;
        else
            parent.right = current;
        handleReorient( item );
    }

    /**
     * Remove from the tree.
     * Not implemented in this version.
     * @param x the item to remove.
     */
    public void remove( Comparable x )
    {
        System.out.println( "Remove is not implemented" );
    }

    /**
     * Find the smallest item  the tree.
     * @return the smallest item or null if empty.
     */
    public Comparable findMin( )
    {
        if( isEmpty( ) )
            return null;

        RedBlackNode itr = header.right;

        while( itr.left != nullNode )
            itr = itr.left;

        return itr.element;
    }

    /**
     * Find the largest item in the tree.
     * @return the largest item or null if empty.
     */
    public Comparable findMax( )
    {
        if( isEmpty( ) )
            return null;

        RedBlackNode itr = header.right;

        while( itr.right != nullNode )
            itr = itr.right;

        return itr.element;
    }

    /**
     * Find an item in the tree.
     * @param x the item to search for.
     * @return the matching item or null if not found.
     */
    public Comparable find( Comparable x )
    {
        nullNode.element = x;
        current = header.right;

        for( ; ; )
        {
            if( x.compareTo( current.element ) < 0 )
                current = current.left;
            else if( x.compareTo( current.element ) > 0 ) 
                current = current.right;
            else if( current != nullNode )
                return current.element;
            else
                return null;
        }
    }

    /**
     * Make the tree logically empty.
     */
    public void makeEmpty( )
    {
        header.right = nullNode;
    }

    /**
     * Test if the tree is logically empty.
     * @return true if empty, false otherwise.
     */
    public boolean isEmpty( )
    {
        return header.right == nullNode;
    }

    /**
     * Print the tree contents in sorted order.
     */
    public void printTree( )
    {
        if( isEmpty( ) )
            System.out.println( "Empty tree" );
        else
            printTree( header.right );
    }

    /**
     * Internal method to print a subtree in sorted order.
     * @param t the node that roots the tree.
     */
    private void printTree( RedBlackNode t )
    {
        if( t != nullNode )
        {
            printTree( t.left );
            System.out.println( t.element );
            printTree( t.right );
        }
    }

    /**
     * Internal routine that is called during an insertion
     * if a node has two red children. Performs flip and rotations.
     * @param item the item being inserted.
     */
    private void handleReorient( Comparable item )
    {
            // Do the color flip
        current.color = RED;
        current.left.color = BLACK;
        current.right.color = BLACK;

        if( parent.color == RED )   // Have to rotate
        {
            grand.color = RED;
            if( ( item.compareTo( grand.element ) < 0 ) !=
                ( item.compareTo( parent.element ) < 0 ) )
                parent = rotate( item, grand );  // Start dbl rotate
            current = rotate( item, great );
            current.color = BLACK;
        }
        header.right.color = BLACK; // Make root black
    }

    /**
     * Internal routine that performs a single or double rotation.
     * Because the result is attached to the parent, there are four cases.
     * Called by handleReorient.
     * @param item the item in handleReorient.
     * @param parent the parent of the root of the rotated subtree.
     * @return the root of the rotated subtree.
     */
    private RedBlackNode rotate( Comparable item, RedBlackNode parent )
    {
        if( item.compareTo( parent.element ) < 0 )
            return parent.left = item.compareTo( parent.left.element ) < 0 ?
                rotateWithLeftChild( parent.left )  :  // LL
                rotateWithRightChild( parent.left ) ;  // LR
        else
            return parent.right = item.compareTo( parent.right.element ) < 0 ?
                rotateWithLeftChild( parent.right ) :  // RL
                rotateWithRightChild( parent.right );  // RR
    }

    /**
     * Rotate binary tree node with left child.
     */
    static RedBlackNode rotateWithLeftChild( RedBlackNode k2 )
    {
        RedBlackNode k1 = k2.left;
        k2.left = k1.right;
        k1.right = k2;
        return k1;
    }

    /**
     * Rotate binary tree node with right child.
     */
    static RedBlackNode rotateWithRightChild( RedBlackNode k1 )
    {
        RedBlackNode k2 = k1.right;
        k1.right = k2.left;
        k2.left = k1;
        return k2;
    }

    private RedBlackNode header;
    private static RedBlackNode nullNode;
        static         // Static initializer for nullNode
        {
            nullNode = new RedBlackNode( null );
            nullNode.left = nullNode.right = nullNode;
        }

    static final int BLACK = 1;    // Black must be 1
    static final int RED   = 0;

        // Used in insert routine and its helpers
    private static RedBlackNode current;
    private static RedBlackNode parent;
    private static RedBlackNode grand;
    private static RedBlackNode great;


        // Test program
    public static void main( String [ ] args )
    {
        RedBlackTree t = new RedBlackTree( new MyInteger( Integer.MIN_VALUE ) );
        final int NUMS = 40000;
        final int GAP  =   307;


        t.printTree(); 

        System.out.println( "Checking... (no more output means success)" );

        for( int i = GAP; i != 0; i = ( i + GAP ) % NUMS )
            t.insert( new MyInteger( i ) );

        if( NUMS < 40 )
            t.printTree( );
        if( ((MyInteger)(t.findMin( ))).intValue( ) != 1 ||
            ((MyInteger)(t.findMax( ))).intValue( ) != NUMS - 1 )
            System.out.println( "FindMin or FindMax error!" );

        for( int i = 1; i < NUMS; i++ )
             if( ((MyInteger)(t.find( new MyInteger( i ) ))).intValue( ) != i )
                 System.out.println( "Find error1!" );
    }
}

我应该向 RedBlackTree 添加项目，并且我应该添加一个 Comparable。这是我第一次接触这种数据类型。我应该传入什么值？

Answer 1

存储在红黑树中的每个 T 类型的对象都应该实现 Comparable 接口(interface)，这意味着它应该具有如下功能:

int compareTo(T o) {
 //returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
}

目的是能够为红黑树内的对象存储和定位提供比较的基础。默认情况下，像 String 或 Integer 这样的简单对象是可比较的，但您也可以使用相同的数据结构来存储任何自定义类的实例，只要它实现 Comparable 接口(interface)即可。