链表

链表

链表的定义

链表是一种线性表，它是在每一个节点里存放下一个节点的位置信息。

单向链表

每个节点包含两个域，一个信息域，一个链接域，这个链接指向链表中的下一个节点，最后一个节点的链接域则指向空值。

# 单链表功能代码实现
class Node(object):
    """节点"""
    def __init__(self, elem):
        self.elem = elem
        self.next = None

class SingleLinkList(object):
    """单链表"""
    def __init__(self, node=None):
        self.__head = node

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

    def length(self):
        """链表长度"""
        # cur游标，用来移动遍历节点
        cur = self.__head
        # count记录数量
        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 append(self, item):
        """链表尾部添加元素, 尾插法"""
        node = Node(item)
        if self.is_empty():   #判断列表是否为空
            self.__head = node
        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
        :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):
                count += 1
                pre = pre.next
            # 当循环退出后，pre指向pos-1位置
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """删除节点"""
        cur = self.__head
        pre = None
        while cur != None:
            if cur.elem == item:
                # 先判断此结点是否是头节点
                # 头节点
                if cur == self.__head:
                    self._head = cur.next
                else:
                    pre.next = cur.next
                break
            else:
                pre = cur
                cur = cur.next

    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

链表与顺序表的对比

链表与顺序表的各种操作复杂度对比：

操作	链表	顺序表
访问元素	O(n)	O(1)
在头部插入/删除	O(1)	O(n)
在尾部插入/删除	O(n)	O(1)
在中间插入/删除	O(n)	O(n)

双向链表

双向链表每个节点有两个链接：一个指向前一个节点，当此节点为第一个节点时，指向空值；另一个指向下一个节点，当此节点为最后一个节点是，指向空值。

# 双向链表功能代码实现
class Node(object):
    """结点"""
    def __init__(self, item):
        self.elem = item
        self.next = None
        self.prev = None
class DoubleLinkList(object):
    """双链表"""
    def __init__(self, node=None):
        self.__head = node

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

    def length(self):
        """链表长度"""
        # cur游标，用来移动遍历节点
        cur = self.__head
        # count记录数量
        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 append(self, item):
        """链表尾部添加元素, 尾插法"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        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
        :param  pos 从0开始
        """
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            cur = self.__head
            count = 0
            while count < pos:
                count += 1
                cur = cur.next
            # 当循环退出后，cur指向pos位置
            node = Node(item)
            node.next = cur
            node.prev = cur.prev
            cur.prev.next = node
            cur.prev = node

    def remove(self, item):
        """删除节点"""
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                # 先判断此结点是否是头节点
                # 头节点
                if cur == self.__head:
                    self.__head = cur.next
                    if cur.next:
                        # 判断链表是否只有一个结点
                        cur.next.prev = None
                else:
                    cur.prev.next = cur.next
                    if cur.next:
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next

    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

单向循环链表

单向循环链表是单链表的一种变形，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。

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

    def length(self):
        """链表长度"""
        if self.is_empty():
            return 0
        # cur游标，用来移动遍历节点
        cur = self.__head
        # count记录数量
        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
        cur = self.__head
        while cur.next != self.__head:
            print(cur.elem, end=" ")
            cur = cur.next
        # 退出循环，cur指向尾节点，但尾节点的元素未打印
        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
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            # 退出循环，cur指向尾节点
            node.next = self.__head
            self.__head = node
            # cur.next = 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 = cur.next
            node.next = self.__head
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加元素
        :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):
                count += 1
                pre = pre.next
            # 当循环退出后，pre指向pos-1位置
            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:
                # 先判断此结点是否是头节点
                if cur == self.__head:
                    # 头节点的情况
                    # 找尾节点
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                else:
                    # 中间节点
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        # 退出循环，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
                pre.next = self.__head

    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，cur指向尾节点
        if cur.elem == item:
            return True
        return False