python链表 —— 单向循环链表的增、删、查

单链表是一个变形的单向循环链表，链表中最后的一个节点的next域不再为None，而是指向链表的头结点

单向循环链表的增、删、查实现

class Node(object):
    def __init__(self, item):
        self.item = item
        self.next = None

class SinCyLinkList(object):
    def __init__(self):
        self.head = None

    def is_empty(self):
        return self.head == None

    def length(self):
        '''链表长度'''
        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
        while cur.next != self.head:
            print(cur.item)
            cur = cur.next

    def add(self, item):
        '''在头部插入节点'''
        node = Node(item)
        if self.head == None:
            self.head = node
            node.next = self.head
        else:
            node.next = self.head
            cur = self.head
            while cur.next != self.head:
                cur = cur.next
            cur.next = node
            self.head = node

    def append(self, item):
        '''在尾部插入节点'''
        node = Node(item)
        if self.head == None:
            self.head = node
            node.next = self.head
        else:
            cur = self.head
            while cur.next != self.head:
                cur = cur.next
            cur.next = node
            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
            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'''
        if self.is_empty():
            return
        cur = self.head
        pre = None
        #若删除的是头节点
        if cur.item == item:
            if cur.next != self.head:
                #先找到尾节点
                while cur.next != self.head:
                    cur = cur.next
                cur.next = self.head.next
                self.head = self.head.next
            else:
                self.head = None
        else:
            pre = self.head
            while cur.next != self.head:
                if cur.item == item:
                    pre.next = cur.next
                    return
                else:
                    pre = cur
                    cur = cur.next
            if cur.item == item:
                pre.next = cur.next

    def search(self, item):
        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 = SinCyLinkList()
    print(ll.head)
    ll.add(1)
    ll.add(2)
    ll.add(3)
    ll.insert(2, 4)
    ll.insert(4,5)
    ll.insert(0, 6)
    print("length:",ll.length())
    print("删除前：")
    ll.travel()
    print(ll.search(3))
    print(ll.search(7))
    print("删除节点")
    ll.remove(1)
    print("遍历链表")
    ll.travel()