python实现数据结构（三）——单向循环链表实现

单向循环链表的结构

单链表的一个变形是单向循环链表，链表中最后一个节点的next域不再为None，而是指向链表的头节点。

代码实现

# 如果要直接使用可以使用deque创建队列(也就是链表)


# 2 节点实现
class Node(object):
    """单链表的结点"""

    def __init__(self, item):
        # item存放数据元素
        self.item = item
        # next是下一个节点的标识
        self.next = None


# 链表实现
class SinCycLinkedlist(object):
    """单向链表实现"""

    def __init__(self):
        """每个链表都有一个头"""
        self.__head = None

    def is_empty(self):
        """判断列表是否为空"""
        return self.__head == None

    def length(self):
        """获取链表长度"""
        if self.is_empty():
            return 0
        count = 1
        cur = self.__head
        while cur.next != self.__head:  # 只要链表块的指向不指向头部，就一直count+1
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历列表"""
        if self.is_empty():
            return
        cur = self.__head
        while cur.next != self.__head:
            print(cur.item)
            cur = cur.next
        print("")

    def add(self, item):
        """头部增加元素"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        else:
            node.next = self.__head
            cur = self.__head
            # 移动到链表尾部，将尾部的next链接到新增元素
            while cur.next != self.__head:
                cur = cur.next
            cur.next = node
            self.__head = node

    def append(self, item):
        """尾部添加元素"""
        node = Node(item)
        # 如果链表为空，将链表头指向node
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        # 不为空的情况下，找到最后一个节点，将他的next链接到node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            cur.next = node
            node.next = self.__head

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

    def remove(self, item):
        """删除节点"""
        if self.is_empty():
            return
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.item == item:
                # 判断删除的节点是不是第一个，如果是第一个
                if cur == self.__head:
                    # 找到尾节点
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                else:  # 中间节点
                    # 将删除节点的前一个节点的next指向删除节点的下一个节点
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next

        if cur.item == item:
            if cur == self.__head:
                # 链表只有一个节点
                self.__head = None
            else:
                # pre.next = cur.next
                pre.next = self.__head

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

        return False

效果演示：

if __name__ == '__main__':
    ll = SinCycLinkedlist()
    ll.add(1)
    ll.add(2)
    ll.append(3)
    ll.insert(2, 4)
    ll.insert(4, 5)
    ll.insert(0, 6)
    print("length:", ll.length())
    ll.travel()
    print(ll.search(3))
    print(ll.search(7))
    ll.remove(1)
    print("length:", ll.length())
    ll.travel()

length: 6
6
2
1
4
3

True
False
length: 5
6
2
4
3