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一、链表

将元素存放在通过链接构造起来的一系列存储块中
在每一节点（数据存储单元）里存放下一个节点的位置信息（地址）

1.1 单链表

又称单向链表
它的每个节点包含两个域，一个信息域（元素域），一个链接域。这个链接指向链表的下一个节点，而最后一个节点的链接域则指向一个空值

• 元素域elem用来存放具体的数据
• 链接域next用来存放下一个节点的位置
• 变量p指向链接的头节点的位置，从p出发就可以找到表中的任意节点

1.1.1 变量实质

=相当于指向，操作的是地址信息

1.1.2 节点实现

eg:

# 节点
class Node(object):
    # 对象属性：item, next
    def __init__(self, item):
        self.item = item
        self.next = None


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

    def is_empty(self):
        """
        链表是否为空
        :return 链表为空返回真
        """
        return self.__head is None

    def length(self):
        """
        计算链表长度
        :return 链表长度
        """
        count = 0
        cur = self.__head
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        if not cur:
            print(None)
        else:
            while cur is not None:
                print(cur.item, end=' ')
                cur = cur.next
            print('')

    def add(self, item):
        """
        链表头部增加元素
        :param item:要添加的具体数据
        """
        node = Node(item)
        node.next = self.__head
        self.__head = node

    def append(self, item):
        """链表尾部增加元素"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next is not None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加元素"""
        # 在头部添加元素
        if pos <= 0:
            self.add(item)
        # 在尾部添加元素
        elif pos >= self.length():
            self.append(item)
        # 在中间添加元素
        else:
            cur = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                cur = cur.next
            node = Node(item)
            node.next = cur.next
            cur.next = node

    def remove(self, item):
        """删除元素"""
        cur = self.__head
        pre = None
        while cur is not None:
            if cur.item == item:
                # 头部找到的元素
                if cur == self.__head:
                    self.__head = cur.next
                else:
                    pre.next = cur.next
                return
            # 不是要找的元素，就移动游标
            pre = cur
            cur = cur.next

    def search(self, item):
        """查看元素是否存在"""
        cur = self.__head
        while cur is not None:
            if cur.item == item:
                return True
            cur = cur.next
        return False


if __name__ == '__main__':
    sll = SingleLinkList()

    print(sll.length())  # 0
    sll.travel()    # None

    sll.append(1)  # 1
    sll.travel()

    sll.append(2)  # 1,2
    sll.travel()

    sll.add(3)     # 3,1,2
    sll.travel()

    sll.insert(0, 4)  # 4,3,1,2
    sll.travel()

    sll.insert(19, 5)  # 4,3,1,2,5
    sll.travel()

    sll.insert(2, 6)  # 4,3,6,1,2,5
    sll.travel()

    sll.remove(4)  # 3,6,1,2,5
    sll.travel()

    sll.remove(5)  # 3,6,1,2
    sll.travel()

    sll.remove(6)  # 3,1,2
    sll.travel()

    sll.remove(3)  # 1,2
    sll.travel()

    sll.remove(1)  # 2
    sll.travel()

    sll.remove(2)  # None
    sll.travel()

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1.2 双向链表

eg:

# 节点
class Node(object):
    # 对象属性：item, pre, next
    def __init__(self, item):
        self.item = item
        self.pre = None
        self.next = None


# 双向链表
class DoubleLinkList(object):
    def __init__(self, node=None):
        self.__head = node

    def is_empty(self):
        """
        链表是否为空
        :return 链表为空返回真
        """
        return self.__head is None

    def length(self):
        """
        计算链表长度
        :return 链表长度
        """
        count = 0
        cur = self.__head
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        if not cur:
            print(None)
        else:
            while cur is not None:
                print(cur.item, end=' ')
                cur = cur.next
            print('')

    def search(self, item):
        """查看元素是否存在"""
        cur = self.__head
        while cur is not None:
            if cur.item == item:
                return True
            cur = cur.next
        return False

# ==============前面的可以直接继承单链表类==============

    def add(self, item):
        """
        链表头部增加元素
        :param item:要添加的具体数据
        """
        node = Node(item)
        node.next = self.__head
        self.__head = node
        # 补充的
        if node.next:
            node.next.pre = node

    def append(self, item):
        """链表尾部增加元素"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next is not None:
                cur = cur.next
            node.pre = cur
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加元素"""
        # 在头部添加元素
        if pos <= 0:
            self.add(item)
        # 在尾部添加元素
        elif pos >= self.length():
            self.append(item)
        # 在中间添加元素
        else:
            cur = self.__head
            count = 0
            while count < pos:
                count += 1
                cur = cur.next
            node = Node(item)
            node.next = cur
            node.pre = cur.pre
            # 特别注意下面的两句代码的先后顺序
            # 先与前面的节点相连，再与后面的节点相连
            cur.pre.next = node
            cur.pre = node

    def remove(self, item):
        """删除元素"""
        cur = self.__head
        while cur is not None:
            if cur.item == item:
                # 头部找到的元素
                if cur == self.__head:
                    self.__head = cur.next
                    if cur.next:
                        self.__head.pre = None
                else:
                    cur.pre.next = cur.next
                    if cur.next:
                        cur.next.pre = cur.pre
                return
            # 不是要找的元素，就移动游标
            cur = cur.next


if __name__ == '__main__':
    sll = DoubleLinkList()

    print(sll.length())  # 0
    sll.travel()    # None

    sll.append(1)  # 1
    sll.travel()

    sll.append(2)  # 1,2
    sll.travel()

    sll.add(3)     # 3,1,2
    sll.travel()

    sll.insert(0, 4)  # 4,3,1,2
    sll.travel()

    sll.insert(19, 5)  # 4,3,1,2,5
    sll.travel()

    sll.insert(2, 6)  # 4,3,6,1,2,5
    sll.travel()

    sll.remove(4)  # 3,6,1,2,5
    sll.travel()

    sll.remove(5)  # 3,6,1,2
    sll.travel()

    sll.remove(6)  # 3,1,2
    sll.travel()

    sll.remove(3)  # 1,2
    sll.travel()

    sll.remove(1)  # 2
    sll.travel()

    sll.remove(2)  # None
    sll.travel()

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1.3 单向循环链表

链表的最后一个节点的next域不再指向None，而是指向链表的头节点

eg:

# 节点
class Node(object):
    # 对象属性：item, next
    def __init__(self, item):
        self.item = item
        self.next = None


# 单向循环链表
class CycleSingleLinkList(object):
    def __init__(self, node=None):
        self.__head = node

    def is_empty(self):
        """
        链表是否为空
        :return 链表为空返回真
        """
        return self.__head is None

    def length(self):
        """
        计算链表长度
        :return 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):
        """遍历整个链表"""
        cur = self.__head
        if self.is_empty():
            print(None)
            return
        while cur.next != self.__head:
            print(cur.item, end=' ')
            cur = cur.next
        print(cur.item)

    def add(self, item):
        """
        链表头部增加元素
        :param item:要添加的具体数据
        """
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        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):
        """链表尾部增加元素"""
        node = Node(item)
        if self.is_empty():
            node.next = node
            self.__head = 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"""
        # 在头部添加元素
        if pos <= 0:
            self.add(item)
        # 在尾部添加元素
        elif pos >= self.length():
            self.append(item)
        # 在中间添加元素
        else:
            cur = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                cur = cur.next
            node = Node(item)
            node.next = cur.next
            cur.next = node

    # 考虑没有节点、只有一个节点
    # 考虑删除元素是头节点、尾节点还是中间节点
    def remove(self, item):
        """删除元素"""
        if self.is_empty():
            return
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.item == item:
                # 头部找到的元素
                if cur == self.__head:
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = cur.next
                else:
                    pre.next = cur.next
                return
            # 不是要找的元素，就移动游标
            pre = cur
            cur = cur.next
        # 退出循环，cur指向尾节点，需要单独处理
        if cur.item == item:
            # 链表只有一个节点
            if cur == self.__head:
                self.__head = None
                return
            pre.next = self.__head

    def search(self, item):
        """查看元素是否存在"""
        if self.is_empty():
            return False
        cur = self.__head
        while cur.next != self.__head:
            if cur.item == item:
                return True
            cur = cur.next
        if cur.item == item:
            return True
        return False


if __name__ == '__main__':
    sll = CycleSingleLinkList()

    print(sll.length())  # 0
    sll.travel()    # None

    sll.append(1)  # 1
    sll.travel()

    sll.append(2)  # 1,2
    sll.travel()

    sll.add(3)     # 3,1,2
    sll.travel()

    sll.insert(0, 4)  # 4,3,1,2
    sll.travel()

    sll.insert(19, 5)  # 4,3,1,2,5
    sll.travel()

    sll.insert(2, 6)  # 4,3,6,1,2,5
    sll.travel()

    sll.remove(4)  # 3,6,1,2,5
    sll.travel()

    sll.remove(5)  # 3,6,1,2
    sll.travel()

    sll.remove(6)  # 3,1,2
    sll.travel()

    sll.remove(3)  # 1,2
    sll.travel()

    sll.remove(1)  # 2
    sll.travel()

    sll.remove(2)  # None
    sll.travel()

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更新中......

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