百度百科的关键词链接是怎样实现的呢

include 'TTrie.php';class wordkey extends TTrie {  function b() {    $t = array_pop($this->buffer);    $this->buffer[] = "<b>$t</b>";  }}$p = new wordkey;$p->set('秦始皇', 'b');$p->set('洛阳', 'b');$t = $p->match('秦始皇东巡洛阳');echo join('', $t);

class TTrie {  protected $buffer = array();  protected $dict = array( array() );  protected $input = 0; //字符串当前偏移  protected $backtracking = 0; //字符串回溯位置  public $debug = 0;  public $savematch = 1;  function set($word, $action='') {	if(is_array($word)) {		foreach($word as $k=>$v) $this->set($k, $v);		return;	}	$p = count($this->dict);	$cur = 0; //当前节点号	foreach(str_split($word) as $c) {		if (isset($this->dict[$cur][$c])) { //已存在就下移			$cur = $this->dict[$cur][$c];			continue;		}		$this->dict[$p]= array(); //创建新节点		$this->dict[$cur][$c] = $p; //在父节点记录子节点号		$cur = $p; //把当前节点设为新插入的		$p++;	}	$this->dict[$cur]['acc'] = $action; //一个词结束，标记叶子节点  }  function getto($ch) {	$i =& $this->input; //字符串当前偏移	$p =& $this->backtracking; //字符串回溯位置	$len = strlen($this->doc);	$t = '';	$this->input++;//	while($this->input<$len && $this->doc{$this->input} != $ch) $t .= $this->doc{$this->input++};//	$t .= $this->doc{$this->input++};	do {		if($this->input >= $len) break;		$t .= $this->doc{$this->input};	}while($this->doc{$this->input++} != $ch);	return trim($t);  }	  function match($s) {	$this->doc =& $s;	$this->buffer = array();	$ret = array();	$cur = 0; //当前节点，初始为根节点	$i =& $this->input; //字符串当前偏移	$p =& $this->backtracking; //字符串回溯位置	$i = $p = 0;	$s .= "\0"; //附加结束符	$len = strlen($s);	$buf = '';	while($i < $len) {		$c = $s{$i};		if(isset($this->dict[$cur][$c])) { //如果存在			$cur = $this->dict[$cur][$c]; //转到对应的位置			if(isset($this->dict[$cur][$s[$i+1]])) {//检查下一个字符是否也能匹配，长度优先				$i++;				continue;			}			if(isset($this->dict[$cur]['acc'])) { //是叶子节点，单词匹配！				if($buf != '') {					$this->buffer[] = $buf;					$buf = '';				}				if($this->savematch) $this->buffer[] = substr($s, $p, $i - $p + 1); //取出匹配位置和匹配的词				$ar = explode(',', $this->dict[$cur]['acc']);				call_user_func_array( array($this, array_shift($ar)), $ar );				$p = $i + 1; //设置下一个回溯位置				$cur = 0; //重置当前节点为根节点			}		} else { //不匹配			$buf .= $s{$p}; //substr($s, $p, $i - $p + 1); //保存未匹配位置和未匹配的内容			$cur = 0; //重置当前节点为根节点			$i = $p; //把当前偏移设为回溯位置			$p = $i + 1; //设置下一个回溯位置		}		$i++; //下一个字符	}	if(trim($buf, "\0")) $this->buffer[] = trim($buf, "\0");	return $this->buffer;  }  function __call($method, $param) {	if($this->debug) printf("偏移:%d 回溯:%d\n", $this->input, $this->backtracking);  }}