python 链表实现 双向链表

Posted 2020-10-31 homle

　　1.  双向链表的定义

　　  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；而另一个指向下一个节点，当此节点为最后一个节点时，指向空值。

　　

　　2.  操作

• 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

　　3.  实现

class Node(object):
    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):
        #判断链表是否为空
        return self.__head is None
        
    def length(self):
        #链表的长度
        #cur游标，用来遍历节点，count记录数量
        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.elem,end=\' \')
            cur = cur.next
        print(\'\')
    def add(self,item):
        #在链表头部添加节点
        node = Node(item)
        node.next = self.__head
        self.__head = node
        node.next.prev = node
        
    def append(self,item):
        #在链表尾部添加节点
        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

　　在链表指定位置插入元素

    def insert(self,pos,item):
        #在链表指定位置添加节点
        # 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
            #当退出循环后,pre指向pos位置
            node = Node(item)
#            node.next = cur
#            node.prev = cur.prev
#            cur.prev.next = node
#            cur.prev = node
            node.prev = cur  #将node的prev指向cur
            node.next = cur.next  #将node的next指向cur的下一个节点
            cur.next.prev = node  #将cur的下一个节点的prev指向node
            cur.next = node  #将cur的next指向node

　　移除和查找节点

    def remove(self,item):
        #移除节点
        cur = self.__head
        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
                    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:
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next
        
    def search(self,item):
        #查找节点
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

　　完整代码：

class Node(object):
    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):
        #判断链表是否为空
        return self.__head is None
        
    def length(self):
        #链表的长度
        #cur游标，用来遍历节点，count记录数量
        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.elem,end=\' \')
            cur = cur.next
        print(\'\')
    def add(self,item):
        #在链表头部添加节点
        node = Node(item)
        node.next = self.__head
        self.__head = node
        node.next.prev = node
        
    def append(self,item):
        #在链表尾部添加节点
        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):
        #在链表指定位置添加节点
        # 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
            #当退出循环后,pre指向pos位置
            node = Node(item)
#            node.next = cur
#            node.prev = cur.prev
#            cur.prev.next = node
#            cur.prev = node
            node.prev = cur  #将node的prev指向cur
            node.next = cur.next  #将node的next指向cur的下一个节点
            cur.next.prev = node  #将cur的下一个节点的prev指向node
            cur.next = node  #将cur的next指向node
        
    def remove(self,item):
        #移除节点
        cur = self.__head
        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
                    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:
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next
        
    def search(self,item):
        #查找节点
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

if __name__ == \'__main__\':
    dll = DoubleLinkList()
    print(dll.is_empty())
    print(dll.length())
    
    dll.append(1)
    print(dll.is_empty())
    print(dll.length())
    
    dll.append(2)
    dll.add(8)
    dll.append(3)
    dll.append(4)
    dll.append(5)
    dll.append(6)
    dll.insert(-1,9)
    dll.travel()
    dll.insert(3,100)
    dll.travel()
    dll.insert(10,200)
    dll.travel()
    dll.remove(100)
    dll.travel()
    dll.remove(9)
    dll.travel()
    dll.remove(200)
    dll.travel()
\'\'\'    
运行结果
True
0
False
1
9 8 1 2 3 4 5 6
9 8 1 2 100 3 4 5 6
9 8 1 2 100 3 4 5 6 200
9 8 1 2 3 4 5 6 200
8 1 2 3 4 5 6 200
8 1 2 3 4 5 6
\'\'\'

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 　　单向循环链表

　　1.  单链表的一个变形是单向循环链表，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。

　　　　

　　2.  操作

• is_empty() 判断链表是否为空
• length() 返回链表的长度
• travel() 遍历
• add(item) 在头部添加一个节点
• append(item) 在尾部添加一个节点
• insert(pos, item) 在指定位置pos添加节点
• remove(item) 删除一个节点
• search(item) 查找节点是否存在

　　3.  实现

class Node(object):
    #单向循环链表节点类实现
    def __init__(self,elem):
        self.elem = elem
        self.next = None

class SingleCycleLinkList(object):
    #单向循环链表类实现
    def __init__(self,node=None):
        self.__head = node
        if node:
            node.next = node
        
    def is_empty(self):
        #判断链表是否为空
        return self.__head == None
        
    def length(self):
        #链表的长度
        if self.is_empty():
            return 0
        #cur游标，用来遍历节点，count记录数量
        cur = self.__head
        count = 1
        while cur.next != self.__head:
            count += 1
            cur = cur.next
        return count
        
    def travel(self):
        #遍历链表
        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):
        #在链表头部添加节点
        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
        
    def append(self,item):
        #在链表尾部添加节点
        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
        
    def insert(self,pos,item):
        #在链表指定位置添加节点
        # 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
            #当退出循环后,pre指向pos-1位置
            node = Node(item)
            node.next = pre.next
            pre.next = node
        
    def remove(self,item):
        #移除节点
        if self.is_empty():
            return 
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.elem == item:
            #先判断此节点是否是头节点
                if cur == self.__head:
                    #头节点的情况
                    #先找到尾节点
                    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
    def search(self,item):
        #查找节点
        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

if __name__ == \'__main__\':
    ll = SingleCycleLinkList()
    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)
    ll.insert(-1,9)
    ll.travel()
    ll.insert(3,100)
    ll.travel()
    ll.insert(10,200)
    ll.travel()
    ll.remove(100)
    ll.travel()
    ll.remove(9)
    ll.travel()
    ll.remove(200)
    ll.travel()
    
\'\'\'
运行结果：
True
0
False
1
9 8 1 2 3 4 5 6
9 8 1 100 2 3 4 5 6
9 8 1 100 2 3 4 5 6 200
9 8 1 2 3 4 5 6 200
8 1 2 3 4 5 6 200
8 1 2 3 4 5 6

\'\'\'
        

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