stringheap.java

这是个JAVA开发的WEB邮箱

/* CVS ID: $Id: StringHeap.java,v 1.2 2000/04/06 08:02:02 wastl Exp $ */
package net.wastl.webmail.misc;

/*
 * StringHeap.java
 *
 * Created: Mon Oct  4 13:28:09 1999
 *
 * Copyright (C) 1999-2000 Sebastian Schaffert
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
/**
 * This class is a simple heap structure for sorting Strings lexicographically.
 * It is mainly used in WebMail for generating a sorted output of Hashkeys.
 *
 * @author Sebastian Schaffert
 * @version
 */

public class StringHeap  {

    int num_entries;
    String[] keys;

    public StringHeap(int capacity) {
	keys=new String[capacity+1];
	num_entries=0;
    }

    /**
     * Insert a key/value pair
     * Reorganize Heap afterwards
     */
    public void insert(String key) {
	keys[num_entries]=key;
	num_entries++;
	
	increase(num_entries);
    }

    /**
     * Return and delete the key with the lowest long value. Reorganize Heap.
     */
    public String next() {
	String ret=keys[0];
	keys[0]=keys[num_entries-1];
	num_entries--;
	
	decrease(1);
	
	return ret;
    }

    public boolean isEmpty() {
	return num_entries==0;
    }

    /**
     * Remove an Object from the Heap.
     * Unfortunately not (yet) of very good complexity since we are doing 
     * a simple linear search here.
     * @param key The key to remove from the heap
     */
    public void remove(String key) {
	for(int i=0;i<num_entries;i++) {
	    if(key.equals(keys[i])) {
		num_entries--;
		int cur_pos=i+1;
		keys[i]=keys[num_entries];
		decrease(cur_pos);
		break;
	    }
	}
    }

    /**
     * Lift an element in the heap structure
     * Note that the cur_pos is actually one larger than the position in the array!
     */
    protected void increase(int cur_pos) {
	while(cur_pos > 1 && keys[cur_pos-1].compareTo(keys[cur_pos/2-1]) < 0) {
	    String tmp1=keys[cur_pos/2-1];keys[cur_pos/2-1]=keys[cur_pos-1];keys[cur_pos-1]=tmp1;
	    cur_pos /= 2;
	}
    }	    

    /**
     * Lower an element in the heap structure
     * Note that the cur_pos is actually one larger than the position in the array!
     */
    protected void decrease(int cur_pos) {
	while((cur_pos*2 <= num_entries && keys[cur_pos-1].compareTo(keys[cur_pos*2-1]) > 0) ||
	      (cur_pos*2+1 <=num_entries && keys[cur_pos-1].compareTo(keys[cur_pos*2]) > 0)) {
	    int lesser_son;
	    if(cur_pos*2+1 <= num_entries) {
		lesser_son=keys[cur_pos*2-1].compareTo(keys[cur_pos*2])<0?cur_pos*2:cur_pos*2+1;
	    } else {
		lesser_son=cur_pos*2;
	    }
	    String tmp1=keys[cur_pos-1];keys[cur_pos-1]=keys[lesser_son-1];keys[lesser_son-1]=tmp1;
	    cur_pos=lesser_son;
	}
    }	    
		
} // StringHeap