php实现LRU缓存机制

class LRUCache {
	/**
	 * @param Integer $capacity
	 */
	public $capacity;
	public $LRUArr=[];
	function __construct($capacity) {
		$this->capacity = $capacity;
	}

	/**
	 * @param Integer $key
	 * @return Integer
	 */
	function get($key) {
	   if(array_key_exists($key,$this->LRUArr)){
		   $tmp = $this->LRUArr[$key];
		   unset($this->LRUArr[$key]);
		   $this->LRUArr[$key]= $tmp;
		   return $tmp;
	   }
	   return -1;
	}

	/**
	 * @param Integer $key
	 * @param Integer $value
	 * @return NULL
	 */
	function put($key, $value) {
		//判断是否在数组中 在就删除 并且把新值插入数组最后
		if(array_key_exists($key,$this->LRUArr)){
			unset($this->LRUArr[$key]);
		}else{
			$len =count($this->LRUArr);
			if($len == $this->capacity){
				//超出则删除第一个元素，将新元素添加到数组尾
				//array_shift 所有的数字键名将改为从零开始计数，文字键名将不变
				//$this->LRUArr = array_slice($this->LRUArr,1,NULL,true);
				foreach($this->LRUArr as $k=>$v){
					unset($this->LRUArr[$k]);
					break;
				}
			}
		}
		$this->LRUArr[$key]=$value;
	}
}
$obj = new LRUCache(2);
$obj->put(1, 1);
$obj->put(2, 2);
$obj->get(1);
$obj->put(3, 3);
$obj->get(2);       // 返回 -1 (未找到)
$obj->put(4, 4);    // 该操作会使得密钥 1 作废
$obj->get(1);       // 返回 -1 (未找到)
$obj->get(3);       // 返回  3
$obj->get(4);       // 返回  4