单向循环链表

单线循环链表
单向循环链表与单向链表的区别就是单向循环链表的尾节点指向了头节点。我们知道，单向链表的尾节点指向None，而单向循环链表指向了头节点，这就是他们之间的区别

单向循环链表的实现

class Node(object):
    """节点"""

    def __init__(self, elem):
        self.elem = elem
        self.next = None

class SingleLinkCycleList(object):
    """单链表"""

    def __init__(self,node=None):
        self._head = node
        if node:
            node.next = node

    def is_empty(self):
        """链表是否为空"""
        return self._head == None

    def length(self):
        """链表长度"""
        if self.is_empty():
            return 0
        cur = self._head
        count = 1
        while cur.next != self._head:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个列表"""
        if self.is_empty():
            return 0
        cur = self._head
        while cur.next != self._head:
            print(cur.elem, end=" ")
            cur = cur.next
        print(cur.elem)
        print("")

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

    def append(self,item):
        """链表尾部添加元素,尾插法"""
        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
            node.next = self._head
            cur.next = node

    def insert(self,pos,item):
        """指定位置添加元素
        :param item: 指定增加的具体元素
        :param pos 从0开始
        """
        if pos <= 0:
            self.add(item)
        elif pos > self.length()-1:
            self.append(item)
        else:
            pre = self._head
            count = 0
            while count < pos-1:
                pre = pre.next
                count += 1
            #循环退出后 pre指向pos-1
            node = Node(item)
            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.elem == item:
                #判断此节点是否是头节点
                if cur == self._head:
                    rear = self._head
                    while rear.next != self._head:
                        rear = rear.next
                    self._head = cur.next
                    rear.next = self._head
                else:
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        if cur.elem == item:
            if cur == self._head:
                 self._head = None
        else:
            pre.next = cur.next

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

单向循环链表检查代码：

if __name__ == "__main__":
 li = SingleLinkCycleList()
 # 检测是否为空
 print(li.is_empty())
 # 查看链表长度
 print(li.length())
 # 向链表尾部增加元素
 li.append(1)
 # 向链表头部增加元素
 li.add(3)
 li.append(2)
 li.append(4)
 li.append(5)
 print(li.length())
 # 遍历链表
 li.travel()
 # 向指定位置增加元素
 li.insert(3, 9)
 li.travel()
 # 删除元素
 li.remove(9)
 li.travel()

代码输出效果如下：

True
0
5
3 1 2 4 5

3 1 2 9 4 5

3 1 2 4 5

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