单向链表

# 用来表示节点
class Node:
    def __init__(self, elem):
        self.elem = elem
        self.next = None
 
# 链表
class SingleLinkList:
    def __init__(self, node=None):
        self.__head = node
    
    # 判断是否为空, __head 为空即为空
    def is_empty(self):
        return self.__head == None

    # 判断长度
    def length(self):
        cur = self.__head # 用来遍历链表
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    # 遍历链表
    def travel(self):
        cur = self.__head # 用来遍历链表
        while cur != None:
            print(cur.elem, end="  ")
            cur = cur.next
        print()
    # 链表头部添加
    def add(self, item):
        node = Node(item)
        node.next = self.__head
        self.__head = node

    # 尾部插入 item 为数据， 在内部封装为节点
    def append(self, item):
        cur = self.__head
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            while cur.next != None: # 指向最后一个节点
                cur = cur.next
            cur.next = node

    def insert(self, pos, item): # insert(2, 100)
        """
            pos 下标，从0开始
        """
　　　　　# 输入的值为负数，默认头插
        if pos <= 0:
            self.add(item)
        elif pos >= self.length() - 1: # 默认尾插
            self.append(item)
        else:
            cur = self.__head
            node = Node(item)
            count = 0
            while count < item - 1:
                cur = cur.next
                count += 1
            node.next = cur.next
            cur.next = node

    # 删除找到的第一个
    def remove(self, item):
        pre = None
        cur = self.__head
        while cur != None:
            if cur.elem == item: 
                # 如果目标节点是头节点
                if pre == None:
                    self.__head = cur.next
                # 其他节点和尾节点
                else:
                    pre.next = cur.next
                return cur.elem
            else:
                pre = cur
                cur = cur.next

    def search(self, item):
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False



if __name__ == "__main__":
    ll = SingleLinkList()
    print(ll.is_empty())
    print(ll.length())

    ll.append(1)
    ll.append(2)
    ll.append(3)
    ll.add(100)
    ll.append(4)
    ll.append(5)
    ll.append(6)
    ll.insert(100, 111)
    ll.insert(-100, 112)
    print(ll.length())
    ll.travel()
    ll.remove(6)
    ll.travel()
    ll.remove(112)
    ll.travel()
    ll.remove(111)
    ll.travel()

True
0
9
112  100  1  2  3  4  5  6  111  
112  100  1  2  3  4  5  111  
100  1  2  3  4  5  111  
100  1  2  3  4  5