문제풀이용 Double LinkedList

class Li<T>{

    class Node<T>{
        Node<T> prev;
        Node<T> next;
        T data;

        Node(T data){
            this.data = data;
        }
    }

    Node<T> head;
    Node<T> tail;
    int size=0;

    void add(T e){
        Node<T> newNode = new Node(e);
        if(size==0){
            head = newNode;
            tail = newNode;
        }else{
            head.prev = newNode;
            newNode.next = head;
            head = newNode;
        }
        size++;
    }
}

find는 head가지고 와서 직접하면 될듯.