一、链表的定义

　　用链接关系显式表示元素之间顺序关系的线性表称为链接表或链表。

二、单链表的python实现

class Node(object):
    """定义节点"""

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

class SingleLinkList(object):
    """单链表操作"""

    def __init__(self, node=None):
        """初始化"""
        self.__head = node

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

    def length(self):
        """链表长度"""
        # 定义游标，用来移动遍历节点
        cur = self.__head
        # 定义计数
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur != None:
            print(cur.elem,end=" ")
            cur = cur.next
        print("")

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

    def append1(self, item):
        """链表尾部添加元素,尾插法"""
        node = Node(item)
        # if self.__head == None:
        if self.is_empty():
            self.__head = node
            return
        else:
            cur = self.__head
            while cur.next != None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加元素
        pos 从0开始
        """
        if pos < 0 :
            # 输入值小于0，默认为头插法
            return self.add(item)
        elif pos > self.length()-1:
            # 输入值大于列表长度，默认为尾插法
            self.append1(item)
        else:
            node = Node(item)
            cur = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                cur = cur.next
            # 当循环退出时，cur指向pos-1的位置
            node.next = cur.next
            cur.next = node

    def remove(self, item):
        """删除节点,只删除第一个找到的数据"""
        cur = self.__head
        pre = None
        while cur != None:
            if cur.elem == item:
                # 先判断此节点是否是头节点
                # if pre == None:
                if cur == self.__head:
                    self.__head = cur.next
                # 删除节点
                else:
                    pre.next = cur.next
                break
            else:
                pre = cur
                cur = cur.next
        return

    def search(self, item):
        """查找节点是否存在"""
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

三、单循环链表的python实现：

class Node(object):
    """定义节点"""

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

class SingleCycleList(object):
    """单向循环链表操作"""

    def __init__(self, node=None):
        """初始化"""
        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"""
        # 定义游标，用来移动遍历节点
        if self.is_empty():
            return 0
        cur = self.__head
        # 定义计数
        count = 1
        while cur.next != self.__head:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        if self.is_empty():
            return 0
        cur = self.__head
        while cur.next != self.__head:
            print(cur.elem, end=" ")
            cur = cur.next
        # 退出循环时，cur指向尾节点，但未打印尾节点元素
        print(cur.elem)

    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
            return
        cur = self.__head
        while cur.next != self.__head:
            cur = cur.next
        # 退出循环时，cur指向尾节点
        node.next = self.__head
        self.__head = node
        cur.next = node

    def append1(self, item):
        """链表尾部添加元素,尾插法"""
        node = Node(item)
        # if self.__head == None:
        if self.is_empty():
            self.__head = node
            node.next = 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
        pos 从0开始
        """
        if pos < 0 :
            # 输入值小于0，默认为头插法
            return self.add(item)
        elif pos > self.length()-1:
            # 输入值大于列表长度，默认为尾插法
            self.append1(item)
        else:
            node = Node(item)
            cur = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                cur = cur.next
            # 当循环退出时，cur指向pos-1的位置
            node.next = cur.next
            cur.next = node

    def remove(self, item):
        """删除节点,只删除第一个找到的数据"""
        if self.is_empty():
            return
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.elem == item:
                # 先判断此节点是否是头节点
                # if pre == None:
                if cur == self.__head:
                    # 头结点的情况，找尾节点
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                # 删除节点
                else:
                    # 中间节点
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        # 退出循环时，cur指向尾节点
        if cur.elem == item:
            if cur == self.__head:
                # 链表只有一个节点
                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.next != self.__head:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        # 退出循环时，cur指向尾节点
        if cur.elem == item:
            return True
        return False

四、双循环链表的python实现：

class Node(object):
    """定义节点"""

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

class DoubleLinkList(object):
    """双链表操作"""

    def __init__(self, node=None):
        """初始化，构造"""
        self.__head = node

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

    def length(self):
        """链表长度"""
        # 定义游标，用来移动遍历节点
        cur = self.__head
        # 定义计数
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur != None:
            print(cur.elem, end=" ")
            cur = cur.next
        print("")

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

    def append1(self, item):
        """链表尾部添加元素,尾插法"""
        node = Node(item)
        # if self.__head == None:
        if self.is_empty():
            self.__head = node
            return
        else:
            cur = self.__head
            while cur.next != None:
                cur = cur.next
            cur.next = node
            node.prev = cur

    def insert(self, pos, item):
        """指定位置添加元素
        pos 从0开始
        """
        if pos < 0:
            # 输入值小于0，默认为头插法
            return self.add(item)
        elif pos > self.length() - 1:
            # 输入值大于列表长度，默认为尾插法
            self.append1(item)
        else:
            node = Node(item)
            cur = self.__head
            count = 0
            while count < pos:
                count += 1
                cur = cur.next
            # 当循环退出时，cur指向pos的位置
            node.next = cur
            node.prev = cur.prev
            cur.prev.next = node
            cur.prev = node

    def remove(self, item):
        """删除节点,只删除第一个找到的数据"""
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                # 先判断此节点是否是头节点
                # if pre == None:
                if cur == self.__head:
                    self.__head = cur.next
                    if cur.next:
                        # 判断链表是否只有一个节点
                        cur.next.prev = None
                else:
                    cur.prev.next = cur.next
                    if cur.next:
                        # 判断是否为尾节点
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next
        return

    def search(self, item):
        """查找节点是否存在"""
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

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