链表的建立

•   #链表的制作(包含功能: 从头部添加数据,从尾部添加数据,在中间插入数据,查看链表长度,遍历链表,反转链表,删除数据)
    
    class Node():
        def __init__(self,item):
        	self.item = item
        	self.next = None
    class Link():
        def __init__(self):
            self.head = None
        def addByHead(self,item):
            node = Node(item)
            node.next = self.head
            self.head = node
        def isEmpty(self):
            return self.head == None
        
        def addByTail(self,item):
            node = Node(item)
            if self.isEmpty(): #链表为空的操作
                self.head = node
                return
            # 链表为非空的操作
            pre = None
            cur = self.head
            while cur:
                pre = cur
                cur = cur.next
            pre.next = node
        def insertNode(self,item,pos):
            node = Node(item)
            pre = None
            cur = self.head
            if pos == 0:
                self.addByHead(node)
                return
    
            for i in range(pos):
                pre = cur
                cur = cur.next
            pre.next = node
            node.next = cur
        def Length(self):
            count =0
            cur = self.head
            while cur:
                cur = cur.next 
                count +=1
            return count
        def removeNode(self,item):
            pre = None
            cur = self.head
            nextnode = cur.next
            if item == self.head.item:
                self.head = self.head.next
                return
            while cur:
                if cur.item == item:
                    pre.next = nextnode
                    return
                pre = cur 
                cur = cur.next
                nextnode = cur.next
                
       def reverse(self):
           pre = None
           cur = self.head
           while cur:
                nextnode = cur.next
                cur.next = pre
                pre = cur
                cur = nextnode
            self.head = pre