单向循环链表

向右看齐 2022-12-21 04:54 226阅读 0赞

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。  
![在这里插入图片描述][20190820175037387.png]

## 操作 ##

*  is\_empty() 判断链表是否为空
 *  length() 返回链表的长度
 *  travel() 遍历
 *  add(item) 在头部添加一个节点
 *  append(item) 在尾部添加一个节点
 *  insert(pos, item) 在指定位置pos添加节点
 *  remove(item) 删除一个节点
 *  search(item) 查找节点是否存在

## 实现 ##

class Node(object):
        """节点"""
        def __init__(self, item):
            self.item = item
            self.next = None
    
    
    class SinCycLinkedlist(object):
        """单向循环链表"""
        def __init__(self):
            self._head = None
    
        def is_empty(self):
            """判断链表是否为空"""
            return self._head == None
    
        def length(self):
            """返回链表的长度"""
            # 如果链表为空，返回长度0
            if self.is_empty():
                return 0
            count = 1
            cur = self._head
            while cur.next != self._head:
                count += 1
                cur = cur.next
            return count
    
        def travel(self):
            """遍历链表"""
            if self.is_empty():
                return
            cur = self._head
            print cur.item,
            while cur.next != self._head:
                cur = cur.next
                print cur.item,
            print ""
    
    
        def add(self, item):
            """头部添加节点"""
            node = Node(item)
            if self.is_empty():
                self._head = node
                node.next = self._head
            else:
                #添加的节点指向_head
                node.next = self._head
                # 移到链表尾部，将尾部节点的next指向node
                cur = self._head
                while cur.next != self._head:
                    cur = cur.next
                cur.next = node
                #_head指向添加node的
                self._head = node
    
        def append(self, item):
            """尾部添加节点"""
            node = Node(item)
            if self.is_empty():
                self._head = node
                node.next = self._head
            else:
                # 移到链表尾部
                cur = self._head
                while cur.next != self._head:
                    cur = cur.next
                # 将尾节点指向node
                cur.next = node
                # 将node指向头节点_head
                node.next = self._head
    
        def insert(self, pos, item):
            """在指定位置添加节点"""
            if pos <= 0:
                self.add(item)
            elif pos > (self.length()-1):
                self.append(item)
            else:
                node = Node(item)
                cur = self._head
                count = 0
                # 移动到指定位置的前一个位置
                while count < (pos-1):
                    count += 1
                    cur = cur.next
                node.next = cur.next
                cur.next = node
    
        def remove(self, item):
            """删除一个节点"""
            # 若链表为空，则直接返回
            if self.is_empty():
                return
            # 将cur指向头节点
            cur = self._head
            pre = None
            # 若头节点的元素就是要查找的元素item
            if cur.item == item:
                # 如果链表不止一个节点
                if cur.next != self._head:
                    # 先找到尾节点，将尾节点的next指向第二个节点
                    while cur.next != self._head:
                        cur = cur.next
                    # cur指向了尾节点
                    cur.next = self._head.next
                    self._head = self._head.next
                else:
                    # 链表只有一个节点
                    self._head = None
            else:
                pre = self._head
                # 第一个节点不是要删除的
                while cur.next != self._head:
                    # 找到了要删除的元素
                    if cur.item == item:
                        # 删除
                        pre.next = cur.next
                        return
                    else:
                        pre = cur
                        cur = cur.next
                # cur 指向尾节点
                if cur.item == item:
                    # 尾部删除
                    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
            if cur.item == item:
                return True
            while cur.next != self._head:
                cur = cur.next
                if cur.item == item:
                    return True
            return False
    
    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()

[20190820175037387.png]: /images/20221120/8979412ab98d4dbdb2737231c646abd0.png