class Node(object):
    """定义节点这个类"""
    def __init__(self,elem):
        self.elem = elem   #创建这个类的对象时就可以给他传入要保存的数据
        self.next = None   #刚开始不知道指向谁，所以置为空

#node = Node(100)

class Singlelinklist(object):
    """定义单链表，这个类里要实现单链表的各种操作，如链表长度，往链表添加元素等"""
    def __init__(self,node=None):    
        self._head = node    #保存头结点，私有属性


    def is_empty(self):
        """链表是否为空"""
        return self._head   #返回的是True or False?

    def length(self):
        """链表长度"""
        cur = self._head    #游标，用来移动遍历节点，刚开始让他等于head也就是和head指向同一个地址
        count = 0        #记录数量
        while cur !=None:
            cur = cur.next
            count += 1
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self._head
        while cur != None:
            #print(self.elem)   错辽，这里的self指的是sll呀
            print(cur.elem,end=" ")  #打印在同一行end="",在Python2中逗号就行了
            cur = cur.next


    def add(self,item):
        """链表头部添加元素,头插法"""
        node = Node(item)
        node.next = self._head
        self._head = node

    def append(self,item):
        """链表尾部添加元素"""
        node = Node(item)
        #if self.is_empty():    #相当于if self_head == None
        if self._head == None:
            self._head = node
        else:
            cur = self._head
            while cur.next != None:
                cur = cur.next
            cur.next = node

    def insert(self,pos,item):
        """指定位置添加元素"""
        node = Node(item)
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            pre = self._head
            count = 0
            while count <(pos-1):
                count += 1
                pre = pre.next
            node.next = pre.next
            pre.next = node

    def remove(self,item):
        """删除节点"""
        cur = self._head
        pre = None
        while cur != None:   #找到要删的节点了就删，没找到的话游标就接着移动
            if cur.elem == item:
                if cur == self._head:
                    self._head = cur.next
                else:
                    pre.next = cur.next
                break
            else:
                pre = cur
                cur = cur.next

    def search(self,item):
        """查看节点是否存在"""
        cur = self._head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

#测试
if __name__ == "__main__":    #只在当前文件下运行时执行
    sll = Singlelinklist()
    print(sll.is_empty())  #None
    print("什么都不添加时的长度：")
    print(sll.length())    #0

    sll.append(1)
    print(sll.is_empty())   #非空，打印的是self._head
    print("添加了1时的长度：")
    print(sll.length())    #1

    sll.append(2)
    sll.append(3)
    sll.append(4)
    sll.append(5)
    sll.append(6)  #1 2 3 4 5 6
    sll.add(10)   #10 1 2 3 4 5 6
    sll.insert(3,100)  #10 1 2 100 3 4 5 6
    sll.insert(10,1000)  #10 1 2 100 3 4 5 6
    sll.remove(10)  #删头结点
    print("开始遍历所有元素：")
    sll.travel()
   
    print("length:",sll.length())

    print(sll.search(6))  #查一下6在不在链表里