class Link():
    def __init__(self):
        self._head = None  # 頭節點

    def travel(self):  # 遍歷整個連結串列
        cur = self._head
        while cur:
            print(cur.item)
            cur = cur.next

    def add(self, item):  # 連結串列頭部插入節點
        node = Node(item)
        node.next = self._head
        self._head = node

    def append(self, item):  # 連結串列尾部追加節點
        node = Node(item)
        if self._head is None:
            self._head = node
            return
        cur = self._head
        while cur.next:
            cur = cur.next
        cur.next = node

    def insert(self, pos, item):  # 指定位置插入節點
        node = Node(item)
        if pos > self.length():
            return
        if pos == 0:
            node.next = self._head
            self._head = node
            return

        pre = None
        cur = self._head
        for i in range(pos):
            pre = cur
            cur = cur.next
        pre.next = node
        node.next = cur

    def remove(self, item):  # 刪除節點
        pre = None
        cur = self._head
        if item == cur.item:
            self._head = cur.next
            return
        while cur:
            if cur.item == item:
                pre.next = cur.next
                break
            pre = cur
            cur = cur.next

    def reverse(self):  # 連結串列的反轉
        pre = None
        node = self._head
        ne_xt = node.next

    def is_empty(self):  # 連結串列是否為空
        return self._head is None

    def length(self):  # 連結串列的長度
        count = 0
        cur = self._head
        while cur:
            count += 1
            cur = cur.next
        return count

    def search(self, item):  # 查詢節點是否存在
        cur = self._head
        find = False
        while cur:
            if cur.item == item:
                find = True
            cur = cur.next
        return find