Python数据结构与算法---单向循环链表

1. 循环链表

循环链表是一种特殊的单链表。实际上，循环链表也很简单。它跟单链表唯一的区别就在尾结点。我们知道，单链表的尾结点指针指向空地址，表示这就是最后的结点了。而循环链表的尾结点指针是指向链表的头结点。它像一个环一样首尾相连，所以叫作“循环”链表。

2. 单向循环链表的实现

# 节点的实现
class Node(object):
    def __init__(self, item):
        self.item = item
        self.next = None


# 单向循环链表的实现
class SingleCycleLinkList(object):

    def __init__(self, node=None):
        if node == None:
            self.__head = node
        else:
            self.__head = node
            node.next = self.__head
            
    def is_empty(self):
        '''is_empty() 链表是否为空'''
        return self.__head == None

    def length(self):
        '''length() 链表长度'''
        long = 0
        cur = self.__head
        if self.__head == None:
            return long
        long += 1
        while cur.next != self.__head:
            long += 1
            cur = cur.next
        return long

    def travel(self):
        '''travel() 遍历整个链表'''
        cur = self.__head
        if self.is_empty():
            return None
        else:
            while cur.next != self.__head:
                print(cur.item, end=' ')
                cur = cur.next
            print(cur.item)

    def append(self, item):
        '''append(item) 链表尾部添加元素'''
        node = Node(item)
        cur = self.__head
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        else:
            while cur.next != self.__head:
                cur = cur.next
            cur.next = node
            node.next = self.__head

    def add(self, item):
        '''add(item) 链表头部添加元素'''
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = self.__head
            # self.append(item)
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            node.next = self.__head
            self.__head = node
            cur.next = self.__head

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

    def search(self, item):
        '''search(item) 查找节点是否存在'''
        cur = self.__head
        if self.is_empty():
            return False
        else:
            while cur.next != self.__head:
                if cur.item == item:
                    return True
                cur = cur.next
            if cur.item == item:
                return True
        return False

    def remove(self, item):
        '''remove(item) 删除节点'''
        cur = self.__head
        pre = self.__head
        if self.is_empty():
            return None
        elif self.length() == 1 and self.__head.item == item:
            self.__head = None
        else:
            while cur.next != self.__head:
                pre = cur
                cur = cur.next
            if self.__head.item == item:
                self.__head = self.__head.next
                cur.next = self.__head
            elif cur.item == item:
                pre.next = self.__head
            else:
                cur = self.__head
                pre = self.__head
                while cur.next != self.__head:
                    if cur.item == item:
                        pre.next = cur.next
                    pre = cur
                    cur = cur.next

3. 小结

通过这堂课的学习，对于循环链表我大概是掌握了，主要还是逻辑问题，逻辑理清了，自然而然就会了。这堂课以及课后训练的成效还是很大的，还是要继续努力学习。