题目： PHP 实现 单词查找树算法
描述：
class TrieST
{private $_root=null;public function search(string $key){$node=$this->_search($this->_root,$key,0);if(is_null($node)){return null;}return $node->getVal();}private function _search($node,string $key,int $keyIndex){if(is_null($node)){return null;}if(strlen($key)==$keyIndex){return $node;}$nextNodePos=$key[$keyIndex];return $this->_search($node->getNextNode($nextNodePos),$key,++$keyIndex);}public function put(string $key,$value){if(is_null($this->_root)){$this->_root=$this->_put($this->_root,$key,$value,0);}$this->_put($this->_root,$key,$value,0);}private function _put($node,string $key,$value,int $keyIndex){if(is_null($node)){$node=new Node();}if(strlen($key)==$keyIndex){$node->setVal($value);return $node;}$nextNodePos=$key[$keyIndex];$nextNode=$this->_put($node->getNextNode($nextNodePos),$key,$value,++$keyIndex);$node->setNextNode($nextNodePos,$nextNode);return $node;}public function keyWithPrefix(string $pre){}
}
