dsl.java

Data Structures and Algorithm Analysis in Java -- Source Code

    package DataStructures;

    // BinarySearchTree class
    //
    // CONSTRUCTION: with a value at least as large as all others
    //
    // ******************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

    /**
     * Implements a deterministic skip list.
     * Note that all "matching" is based on the compareTo method.
     * @author Mark Allen Weiss
     */
    public class DSL
    {
        /**
         * Construct the DSL.
         * @param inf the largest Comparable.
         */
        public DSL( Comparable inf )
        {
            infinity = inf;
            bottom = new SkipNode( null );
            bottom.right = bottom.down = bottom;
            tail   = new SkipNode( infinity );
            tail.right = tail;
            header = new SkipNode( infinity, tail, bottom );
        }

        /**
         * Insert into the DSL.
         * @param x the item to insert.
         */
        public void insert( Comparable x )
        {
            SkipNode current = header;

            bottom.element = x;
            while( current != bottom )
            {
                while( current.element.compareTo( x ) < 0 )
                    current = current.right;

                // If gap size is 3 or at bottom level and
                // must insert, then promote middle element
                if( current.down.right.right.element.compareTo( current.element ) < 0 )
                {
                    current.right = new SkipNode( current.element, current.right,
                                                  current.down.right.right );
                    current.element = current.down.right.element;
                }
                else
                    current = current.down;
            }

            // Raise height of DSL if necessary
            if( header.right != tail )
                header = new SkipNode( infinity, tail, header );
        }

        /**
         * Remove from the DSL. Unimplemented.
         * @param x the item to remove.
         */
        public void remove( Comparable x )
        {
            System.out.println( "Sorry, remove unimplemented" );
        }

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

            SkipNode current = header;
            while( current.down != bottom )
                current = current.down;

            return elementAt( current );
        }

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

            SkipNode current = header;
            for( ; ; )
                 if( current.right.right != tail )
                     current = current.right;
                 else if( current.down != bottom )
                     current = current.down;
                 else
                     return elementAt( current );
        }

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

            bottom.element = x;
            for( ; ; )
                if( x.compareTo( current.element ) < 0 )
                    current = current.down;
                else if( x.compareTo( current.element ) > 0 )
                    current = current.right;
                else
                    return elementAt( current );
        }

        /**
         * Make the DSL logically empty.
         */
        public void makeEmpty( )
        {
            header.right = tail;
            header.down = bottom;
        }

        /**
         * Test if the DSL is logically empty.
         * @return true if empty, false otherwise.
         */
        public boolean isEmpty( )
        {
            return header.right == tail && header.down == bottom;
        }

        /**
         * Internal method to get element field.
         * @param t the node.
         * @return the element field, or null if t is null.
         */
        private Comparable elementAt( SkipNode t )
        {
            return t == bottom ? null : t.element;
        }

        /**
         * Print the DSL.
         */
        private void printList( )
        {
            SkipNode current = header;

            while( current.down != bottom )
                 ;

            while( current.right != tail )
            {
                System.out.println( current.element );
                current = current.right;
            }
        }

          /** The DSL header. */
        private SkipNode header;
        private Comparable infinity;
        private SkipNode bottom = null;
        private SkipNode tail   = null;
       

            // Test program
        public static void main( String [ ] args )
        {
            DSL t = new DSL( new MyInteger( 100000000 ) );
            final int NUMS = 4000;
            final int GAP  =   37;

            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.printList( );
            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!" );
            if( t.find( new MyInteger( 0 ) ) != null )
                System.out.println( "Find error2!" );
            if( t.find( new MyInteger( NUMS + 10 ) ) != null )
                System.out.println( "Find error2!" );
    }
}