python数据结构与算法第七天【链表】

1.链表的定义

如图：

注意：

（1）线性表包括顺序表和链表

（2）顺序表是将元素顺序地存放在一块连续的存储区里

（3）链表是将元素存放在通过链构造的存储快中

2. 单向链表的实现

#!/usr/bin/env python
# _*_ coding:UTF-8 _*_

class Node(object):

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

class SingleLinkList(object):
    '''单向链表'''
    def __init__(self, node=None):
        self.__head = node

    def add(self, item):
        '''向单向链表的头部添加元素'''
        node = Node(item)
        node.next = self.__head
        self.__head = node
        return True

    def insert(self, pos, item):
        '''向单向链表指定位置插入元素'''
        if pos <= 0:
            self.add(item)
        elif pos > self.length() -1:
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while pos - 1 > count:
                count += 1
                pre = pre.next
            node.next = pre.next
            pre.next = node
        return True

    def append(self, item):
        '''向单向链表的尾部追加元素'''
        node = Node(item)
        cur = self.__head
        while cur != None:
            if cur.next != None:
                cur = cur.next
            else:
                break
        cur.next = node
        return True

    def remove(self, item):
        '''删除元素'''
        pre = None
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                if pre != None:
                    pre.next = cur.next
                else:
                    self.__head = cur.next
                break
            else:
                pre = cur
                cur = cur.next
        return False

    def search(self, item):
        '''指定元素搜索'''
        cur = self.__head
        index = 0
        while cur != None:
            if cur.elem != item:
                cur = cur.next
                index += 1
            else:
                return index
        return -1

    def travel(self):
        '''遍历打印单向链表的值'''
        cur = self.__head
        str = ''
        while cur != None and cur.elem != None:
            str += '%s' % cur.elem
            cur = cur.next
        return str

    def length(self):
        '''返回单向链表的长度'''
        cur = self.__head
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

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

if __name__ == "__main__":
    singleLinkList = SingleLinkList()
    print singleLinkList.is_empty()
    print singleLinkList.length()

    singleLinkList.add(1)
    singleLinkList.insert(0, 2)
    singleLinkList.append(3)

    print singleLinkList.is_empty()
    print singleLinkList.length()

    print singleLinkList.travel()
    print singleLinkList.search(3)

    singleLinkList.remove(2)
    print singleLinkList.travel()

结果如下：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/bat_day3/link_list_test.py
True
0
False
3
213
2

Process finished with exit code 0

3.链表与顺序表的对比

操作	链表	顺序表
访问	O(n)	O(1)
头插法	O(1)	O(n)
尾插法	O(n)	O(1)
指定位置插入法	O(n)	O(n)
存储	可以存储在分散的存储空间中；需要存放下一元素的地址，导致占用内存较大	只能存放在连续的存储空间中；无需存放下一元素的地址

4.单向循环链表的实现

#!/usr/bin/env python
#! _*_ coding:UTF-8 _*_

class Node(object):
    '''链表的节点'''
    def __init__(self, elem):
        '''构造方法'''
        self.elem = elem
        self.next = None

class SingleCycleLinkList(object):
    '''单向循环链表'''
    def __init__(self, node=None):
        '''构造方法'''
        self.__head = node
        if node != None:
            node.next = node

    def is_empty(self):
        '''判断单向循环链表是否为空'''
        return self.__head == None

    def length(self):
        '''返回单向循环链表的长度'''
        if self.is_empty():
            return 0

        cur = self.__head
        count = 1
        while cur.next != self.__head:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        '''遍历单向循环链表'''
        if self.is_empty():
            return

        cur = self.__head
        str = ''
        while cur.next != self.__head:
            str += '%s ' % cur.elem
            cur = cur.next
        str += '%s' % cur.elem
        return str

    def add(self, item):
        '''单向循环链表头部插入元素'''
        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 = self.__head
            self.__head = node
            cur.next = node

        return True

    def append(self, item):
        '''向单向循环链表尾部插入元素'''
        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 = self.__head
            cur.next = node

        return True

    def insert(self, pos, item):
        '''向单向链表指定位置插入元素'''
        if pos <= 0:
            self.add(item)
        elif pos > self.length() -1:
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while pos - 1 > count:
                count += 1
                pre = pre.next
            node.next = pre.next
            pre.next = node
        return True

    def remove(self, item):
        '''删除单向循环链表中元素'''
        if self.is_empty():
            return True
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.elem == item:
                if cur == self.__head:
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                else:
                    pre.next = cur.next
                break

            else:
                pre = cur
                cur = cur.next

        if cur.item == item:
            if cur == self.__head:
                self.__head = None
            else:
                pre.next = cur.next
        return True

4.双向链表的实现

class Node(object):
    """双向链表节点"""
    def __init__(self, item):
        self.item = item
        self.next = None
        self.prev = None

class DLinkList(object):
    """双向链表"""
    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"""
        cur = self._head
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历链表"""
        cur = self._head
        while cur != None:
            print cur.item,
            cur = cur.next
        print ""

    def add(self, item):
        """头部插入元素"""
        node = Node(item)
        if self.is_empty():
            # 如果是空链表，将_head指向node
            self._head = node
        else:
            # 将node的next指向_head的头节点
            node.next = self._head
            # 将_head的头节点的prev指向node
            self._head.prev = node
            # 将_head 指向node
            self._head = node

    def append(self, item):
        """尾部插入元素"""
        node = Node(item)
        if self.is_empty():
            # 如果是空链表，将_head指向node
            self._head = node
        else:
            # 移动到链表尾部
            cur = self._head
            while cur.next != None:
                cur = cur.next
            # 将尾节点cur的next指向node
            cur.next = node
            # 将node的prev指向cur
            node.prev = cur

    def search(self, item):
        """查找元素是否存在"""
        cur = self._head
        while cur != None:
            if cur.item == item:
                return True
            cur = cur.next
        return False

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
            # 将node的prev指向cur
            node.prev = cur
            # 将node的next指向cur的下一个节点
            node.next = cur.next
            # 将cur的下一个节点的prev指向node
            cur.next.prev = node
            # 将cur的next指向node
            cur.next = node

def remove(self, item):
        """删除元素"""
        if self.is_empty():
            return
        else:
            cur = self._head
            if cur.item == item:
                # 如果首节点的元素即是要删除的元素
                if cur.next == None:
                    # 如果链表只有这一个节点
                    self._head = None
                else:
                    # 将第二个节点的prev设置为None
                    cur.next.prev = None
                    # 将_head指向第二个节点
                    self._head = cur.next
                return
            while cur != None:
                if cur.item == item:
                    # 将cur的前一个节点的next指向cur的后一个节点
                    cur.prev.next = cur.next
                    # 将cur的后一个节点的prev指向cur的前一个节点
                    cur.next.prev = cur.prev
                    break
                cur = cur.next

if __name__ == "__main__":
    ll = DLinkList()
    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(4)
    ll.remove(1)
    print "length:",ll.length()
    ll.travel()

注意：

is_empty() 链表是否为空

length() 链表长度

travel() 遍历链表

add(item) 链表头部添加

append(item) 链表尾部添加

insert(pos, item) 指定位置添加

remove(item) 删除节点

search(item) 查找节点是否存在