python---单链表的常用操作

class Node(object):
    """结点"""

    def __init__(self, data):
        self.data = data
        self.next = None

class SingleLinkList(object):
    """单链表"""

    def __init__(self, node=None):
        # 头结点设置为私有变量
        self.__head = node

    def is_empty(self):
        """链表是否为空"""
        return self.__head is None

    def length(self):
        """链表长度"""
        cur = self.__head
        count = 0
        while cur is not None:
            cur = cur.next
            count += 1
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur is not None:
            print(cur.data, end="")
            cur = cur.next
        print()

    def add(self, item):
        """头插法, 在链表头部添加结点"""
        node = Node(item)
        node.next = self.__head
        self.__head = node

    def append(self, item):
        """尾插法, 在链表尾部添加结点"""
        node = Node(item)
        # 空链表时, 直接指向要添加的结点
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next is not None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加结点"""
        # 指定位置pos在第一个元素之前,执行头插法
        if pos <= 0:
            self.add(item)
        # 指定位置超过链表尾部, 执行尾插法
        elif pos > self.length() - 1:
            self.append(item)
        else:
            # 指定位置的前一个结点
            pre = self.__head
            node = Node(item)
            count = 0
            while count < (pos - 1):
                pre = pre.next
                count += 1
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """删除结点"""
        cur = self.__head
        pre = None
        while cur is not None:
            # 找到了要删除的结点
            if cur.data == item:
                # 要删除的结点是头结点
                if cur == self.__head:
                    # 将头节点指向头结点的后一个结点
                    self.__head = cur.next
                # 要删除的结点不是头结点
                else:
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next

    def search(self, item):
        """查找结点是否存在"""
        cur = self.__head
        while cur is not None:
            if cur.data == item:
                return True
            cur = cur.next
        return False

if __name__ == '__main__':
    sll = SingleLinkList()
    print(sll.is_empty())
    print(sll.length())
    sll.append(1)
    sll.append(2)
    sll.append(3)
    sll.append(4)
    sll.append(5)
    sll.travel()   # 12345
    print(sll.length())   # 5
    sll.add(99)           # 99 12345
    sll.travel()
    print(sll.length())   # 6
    print(sll.search(6))  # False
    print(sll.search(4))  # True
    sll.remove(3)
    sll.travel()   # 99 1245