单链表英语单词统计（列出所有单词及其出现次数）

原创。
可以调用LinkedList 类的 方法 orderInsert(), 以字母大小的顺序储存 英文字符串。 
同时记录 英文单词出现的次数
The class LinkedList allows an application to store strings in alphabetical order 
by calling orderInsert().  The frequency for each word is also provided.
测试字符串数组：
$city =array("Wuhan", "Beijing", "Shanghai","Thunder Bay",
 "Tianjin", "Changsha", "Kunming", "Edmonton", "Glasgow",
 "Gongyi","Tokyo","New York","Ottawa","Moskow","Edmonton",
 "Glasgow","Edinburgh","Thunder Bay","New Delhi","Edinburgh",
  "Edmonton", "Glasgow", "Edmonton","Glasgow"); 
输出结果：
Beijing(1) Changsha(1) Edinburgh(2) Edmonton(4) Glasgow(4) 
Gongyi(1) Kunming(1) Moskow(1) New Delhi(1) New York(1) 
Ottawa(1) Shanghai(1) Thunder Bay(2) Tianjin(1) Tokyo(1) Wuhan(1)

1. [代码]只限于英文（德文...？）单词。    

  <meta charset="utf-8" />
<?
/**
 * The class LinkedList allows an application to store strings in
 * alphabetical order by calling orderInsert().
 * 此处定义的 LinkedList 类，可以调用它的 方法 orderInsert(),来以字母
 * 大小的顺序储存 英文字符串。
 * The frequency for each word is also provided.
 * 同时记录 英文单词出现的次数
 * 作者： 许同春 author Tongchun Xu 
 * @开源中国 Open Source, China communiity
 * 完成日期：2016年6月11日 completion date: 11 June, 2016
 */
class Node{
    public $data;
	public $frequency;
    public $next;
    function __construct($data, $next = null, $frequency = 1){
        $this->data = $data; //英文字符串
        $this->next = $next; //指向后继结点的指针
		$this->frequency=$frequency; //英文字符串出现的次数
    }    
}

class LinkedList{
    private $head; //单链表的头结点，不存储数据
 function __construct(){//单链表的构造方法
 	//头结点的数据为"傀儡", 不代表 任何数据
    $this->head = new Node("dummy 傀儡"); 
    $this->first = null;
    }

 function isEmpty(){ 
        return ($this->head->next == null);
    }	
/*	orderInsert($data) 方法， 
 *  按给定字符串 $data 的大小, 将其安插到适当的位置，	
 *  以保证单链表中字符串的存储，始终是有序的。 
 */
 function orderInsert($data){
	$p = new Node($data);	
    if($this->isEmpty()){
        $this->head->next = $p;
    }
    else {
	$node= $this->find($data);
	if(!$node){
    $q = $this->head;
    while($q->next != NULL && strcmp($data, $q->next->data)> 0 ){
    $q = $q->next;
		}
        $p->next = $q->next; 
		$q->next = $p;
    }else
	$node->frequency++;
	}
 }

 function find($value){//查询是否有给定的字符串
        $q = $this->head->next;
        while($q->next != null){
        if(strcmp($q->data,$value)==0){
				break;
			}
            $q = $q->next;    
        }
		if ($q->data == $value)
        return $q; 
		else
		return null;
    }

 function traversal(){//遍历单链表
		if(!$this->isEmpty()){
        $p=$this->head->next;
        echo $p->data."(".$p->frequency.") ";
        while($p->next != null){
			$p=$p->next;
			echo $p->data."(".$p->frequency.") ";
			}			
    	}else
		echo "链表为空！";
	}
} 

$ll = new LinkedList();
$city =array("Wuhan", "Beijing", "Shanghai","Thunder Bay",
 "Tianjin", "Changsha", "Kunming", "Edmonton", "Glasgow",
 "Gongyi","Tokyo","New York","Ottawa","Moskow","Edmonton",
 "Glasgow","Edinburgh","Thunder Bay","New Delhi","Edinburgh",
  "Edmonton", "Glasgow", "Edmonton","Glasgow"); 
for ($i=0;$i<count($city);$i++)
$ll->orderInsert($city[$i]);
$ll->traversal();
?>