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Python 链表

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Symbols count in article: 2.1k Reading time ≈ 2 mins.

链表的基本结构：

image-20220831102428767

  • 节点：每个节点有两个部分，左边部分称为值域，用来存放用户数据；右边部分称为指针域，用来存放指向下一个元素的指针。

  • head：head节点永远指向第一个节点

  • tail：tail永远指向最后一个节点

  • None：链表中最后一个节点的指针域为None值

该代码来源：Python数据结构与算法03——单链表、双链表、单项循环链表

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class Node(object):  # 定义节点类
    def __init__(self,elem):
        self.elem = elem 
        self.next = None
    

class SingleLinkList(object):
    # 定义单链表类
    def __init__(self,node=None):
        self._head = node
    
    def is_empty(self):
        return self._head == None
    
    def length(self):
        # 链表长度
        # cur 游标，用于移动遍历节点
        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
        node = Node(item)
        if self.is_empty():
            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:
                # 先判断此节点是否是头节点
                # 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


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

        ll.append(1)
        print(ll.is_empty())
        print(ll.length())

        ll.append(2)
        ll.add(8)
        ll.append(3)
        ll.append(4)
        ll.append(5)
        ll.append(6)
        # 8 1 2 3 4 5 6 
        ll.insert(-1,9)  # 9 8 1 23456
        ll.travel()
        ll.insert(3,100) # 9 8 1 100 2 3456
        ll.travel()
        ll.insert(10,200) # 9 8 1 100 23456 200
        ll.travel()
        ll.remove(100)
        ll.travel()
        ll.remove(9)
        ll.travel()
        ll.remove(200)
        ll.travel()
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