数据结构——单向循环链表及Python实现

单向循环链表

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。

Python实现

# coding:utf-8

class Node(object):
    """节点"""
    def __init__(self, elem):
        self.elem = elem
        self.next = None


class SingleCycleLinkList(object):
    """单向循环链表"""
    def __init__(self, node=None):
        self.__head = node
        if node:
            node.next = node

    def is_empty(self):
        # 判断链表是否为空
        return self.__head is None

    def length(self):
        # 返回链表的长度
        if self.is_empty():
            return 0
        else:
            count = 0
            cur = self.__head
            while cur.next != self.__head:
                count += 1
                cur = cur.next
            # while循环结束后，cur指向尾节点
            return (count + 1)

    def travel(self):
        # 遍历
        if self.is_empty():
            return
        else:
            cur = self.__head
            while cur.next != self.__head:
                print(cur.elem, end=" ")
                cur = cur.next
            # while循环结束后，cur指向尾节点
            print(cur.elem)
            print("")

    def add(self, item):
        # 在头部添加一个节点
        node = Node(item)
        if self.is_empty():
            node.next = node
            self.__head = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            # while循环结束后，cur指向尾节点
            node.next = self.__head
            cur.next = node
            self.__head = node

    def append(self, item):
        # 在尾部添加一个节点
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            # while循环结束后，cur指向尾节点
            cur.next = node
            node.next = self.__head

    def insert(self, pos, item):
        # 在指定位置pos添加节点
        if pos <= 0:
            self.add(item)
        elif pos >= self.length():
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                pre = pre.next
            # while循环结束后，pre指向pos-1
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        # 删除一个节点
        if self.is_empty():
            return
        pre = None
        cur = self.__head
        while cur.next != self.__head:
            # 除了尾节点外的节点，执行以下操作
            if cur.elem == item:
                # 先找到尾节点rear
                rear = self.__head
                while rear.next != self.__head:
                    rear = rear.next
                if self.__head == cur:
                    # 如果要删除的是头节点
                    rear.next = cur.next
                    self.__head = cur.next
                else:
                    # 如果要删除的是中间节点
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        # while循环结束后，cur指向尾节点，pre指向尾节点前一个节点
        # 对尾节点，执行以下操作
        if cur.elem == item:
            if cur == self.__head:
                # 如果链表只有一个节点
                self.__head = None
            else:
                pre.next = cur.next
            return
        else:
            return

    def search(self, item):
        # 查找节点是否存在
        if self.is_empty():
            return False
        cur = self.__head
        while cur.next != self.__head:
            # 除了尾节点外的节点，执行以下操作
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        # while循环结束后，cur指向尾节点
        # 对尾节点，执行以下操作
        if cur.elem == item:
            return True
        else:
            return False

# 测试
if __name__ == "__main__":
    ll = SingleCycleLinkList()
    print(ll.is_empty())
    print(ll.length())

    ll.append(1)
    print(ll.is_empty())
    print(ll.length())

    ll.append(2)
    ll.add(8)
    ll.append(3)
    ll.append(4)
    ll.append(5)
    ll.append(6)
    # 8 1 2 3 4 5 6
    ll.insert(-1, 9) # 9 8 1 2 3 4 5 6
    ll.travel()
    ll.insert(2, 100) # 9 8 100 1 2 3 4 5 6
    ll.travel()
    ll.insert(10, 200) # 9 8 100 1 2 3 4 5 6 200
    ll.travel()
    ll.remove(100)
    ll.travel()
    ll.remove(9)
    ll.travel()
    ll.remove(200)
    ll.travel()
    ll.add(0)
    ll.travel()
    print(ll.search(6))