问：在双向链表的中间插入新节点的程序。

2025年3月17日 | 阅读 12 分钟

说明

在此程序中，我们创建一个双向链表，并在列表的中间插入一个新节点。如果列表为空，则 head 和 tail 都将指向新节点。如果列表不为空，那么我们将计算列表的大小并除以 2，以获得需要插入新节点的中间点。

Program to insert a new node at the middle of doubly linked list

考虑上面的图，需要在列表中间添加一个新节点。首先，我们计算大小，在这种情况下为 4。因此，为了获得中间点，我们将其除以 2 并将其存储在变量 mid 中。节点 current 将指向 head。首先，我们遍历列表，直到 current 指向 mid 位置。定义另一个节点 temp，它指向 current 之后的节点。在 current 和 temp 之间插入新节点。

算法

定义一个 Node 类，它表示列表中的一个节点。它将有三个属性：数据、previous 指向前一个节点，以及 next 指向下一个节点。
为创建双向链表定义另一个类，它有两个节点：head 和 tail。最初，head 和 tail 将指向 null。
addNode() 将向列表中添加节点。
1. 它首先检查头节点是否为 null，然后将节点作为头节点插入。
2. 头节点和尾节点都将指向新添加的节点。
3. 头节点的前一个指针将指向 null，尾节点的下一个指针将指向 null。
4. 如果头节点不为 null，则新节点将插入到列表的末尾，使得新节点的前一个指针将指向尾节点。
5. 新节点将成为新的尾节点。尾节点的下一个指针将指向 null。
addInMid() 将向列表的中间添加一个节点。
1. 它首先检查 head 是否为 null（空列表），然后它将节点插入为 head。
2. 头节点和尾节点都将指向新添加的节点。
3. 如果列表不为空，那么我们计算大小并将其除以 2 以获得中点。
4. 定义节点 current，它将指向 head，并遍历列表，直到 current 指向 mid 节点。
5. 定义另一个节点 temp，它将指向 current 的下一个节点。
6. 新节点将插入在 current 之后和 temp 之前，使得 current 指向新节点，新节点指向 temp。
display() 将显示列表中存在的所有节点。
1. 定义一个新节点“current”，它将指向头节点。
2. 打印 current.data 直到 current 指向 null。
3. 在每次迭代中，current 将指向列表中的下一个节点。

解决方案

Python

#Represent a node of doubly linked list
class Node:
    def __init__(self,data):
        self.data = data;
        self.previous = None;
        self.next = None;
        
class InsertMid:
    #Represent the head and tail of the doubly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        self.size = 0;
        
    #addNode() will add a node to the list
    def addNode(self, data):
        #Create a new node
        newNode = Node(data);
        
        #If list is empty
        if(self.head == None):
            #Both head and tail will point to newNode
            self.head = self.tail = newNode;
            #head's previous will point to None
            self.head.previous = None;
            #tail's next will point to None, as it is the last node of the list
            self.tail.next = None;
        else:
            #newNode will be added after tail such that tail's next will point to newNode
            self.tail.next = newNode;
            #newNode's previous will point to tail
            newNode.previous = self.tail;
            #newNode will become new tail
            self.tail = newNode;
            #As it is last node, tail's next will point to None
            self.tail.next = None;
        #Size will count the number of nodes present in the list
        self.size = self.size + 1;
        
    #addInMid() will add a node to the middle of the list
    def addInMid(self, data):
        #Create a new node
        newNode = Node(data);
        
        #If list is empty
        if(self.head == None):
            #Both head and tail will point to newNode
            self.head = self.tail = newNode;
            #head's previous will point to None
            self.head.previous = None;
            #tail's next point to None, as it is the last node of the list
            self.tail.next = None;
        else:
            #current will point to head
            current = self.head;
            
            #Store the mid position of the list
            mid = (self.size//2) if(self.size % 2 == 0)  else ((self.size+1)//2);
            
            #Iterate through list till current points to mid position
            for i in range(1, mid):
                current = current.next;
                
            #Node temp will point to node next to current
            temp = current.next;
            temp.previous = current;
            
            #newNode will be added between current and temp
            current.next = newNode;
            newNode.previous = current;
            newNode.next = temp;
            temp.previous = newNode;
        self.size = self.size + 1;
            
    #display() will print out the nodes of the list
    def display(self):
        #Node current will point to head
        current = self.head;
        if(self.head == None):
            print("List is empty");
            return;
        while(current != None):
            #Prints each node by incrementing pointer.
            print(current.data),
            current = current.next;
            
        print();
        
dList = InsertMid();
#Add nodes to the list
dList.addNode(1);
dList.addNode(2);
 
print("Original list: ");
dList.display();
 
#Adding node '3' in the middle
dList.addInMid(3);
print( "Updated List: ");
dList.display();
 
#Adding node '4' in the middle
dList.addInMid(4);
print("Updated List: ");
dList.display();
 
#Adding node '5' in the middle
dList.addInMid(5);
print("Updated List: ");
dList.display();

输出

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

C

#include <stdio.h>
 
//Represent a node of the doubly linked list

struct node{
    int data;
    struct node *previous;
    struct node *next;
};    
 
int size = 0;
//Represent the head and tail of the doubly linked list
struct node *head, *tail = NULL;
 
//addNode() will add a node to the list
void addNode(int data) {
    //Create a new node
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    
    //If list is empty
    if(head == NULL) {
        //Both head and tail will point to newNode
        head = tail = newNode;
        //head's previous will point to NULL
        head->previous = NULL;
        //tail's next will point to NULL, as it is the last node of the list
        tail->next = NULL;
    }
    else {
        //newNode will be added after tail such that tail's next will point to newNode
        tail->next = newNode;
        //newNode's previous will point to tail
        newNode->previous = tail;
        //newNode will become new tail
        tail = newNode;
        //As it is last node, tail's next will point to NULL
        tail->next = NULL;
    }
    //Size will count the number of nodes present in the list
    size++;
}
 
//addInMid() will add a node to the middle of the list
void addInMid(int data) {
    //Create a new node
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    
    //If list is empty
    if(head == NULL) {
        //Both head and tail will point to newNode
        head = tail = newNode;
        //head's previous will point to NULL
        head->previous = NULL;
        //tail's next point to NULL, as it is the last node of the list
        tail->next = NULL;
    }
    else {
        //current will point to head
        struct node *current = head, *temp = NULL;
        
        //Store the mid position of the list
        int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);    
        
        //Iterate through list till current points to mid position
        for(int i = 1; i < mid; i++){
            current = current->next;
        }
        
        //Node temp will point to node next to current
        temp = current->next;
        temp->previous = current;
        
        //newNode will be added between current and temp
        current->next = newNode;
        newNode->previous = current;
        newNode->next = temp;
        temp->previous = newNode;
    }
    size++;
}
 
//display() will print out the nodes of the list
void display() {
    //Node current will point to head
    struct node *current = head;
    if(head == NULL) {
        printf("List is empty\n");
        return;
    }
    while(current != NULL) {
        //Prints each node by incrementing pointer.
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}
    
int main()
{
    //Add nodes to the list
    addNode(1);
    addNode(2);
    
    printf("Original list: \n");
    display();
    
    //Adding node '3' in the middle
    addInMid(3);
    printf( "Updated List: \n");
    display();
    
    //Adding node '4' in the middle
    addInMid(4);
    printf("Updated List: \n");
    display();
    
    //Adding node '5' in the middle
    addInMid(5);
    printf("Updated List: \n");
    display();
 
    return 0;
}

输出

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

JAVA

public class InsertMid {
    
    //Represent a node of the doubly linked list

    class Node{
        int data;
        Node previous;
        Node next;
        
        public Node(int data) {
            this.data = data;
        }
    }
    
    public int size = 0;
    //Represent the head and tail of the doubly linked list
    Node head, tail = null;
    
    //addNode() will add a node to the list
    public void addNode(int data) {
        //Create a new node
        Node newNode = new Node(data);
        
        //If list is empty
        if(head == null) {
            //Both head and tail will point to newNode
            head = tail = newNode;
            //head's previous will point to null
            head.previous = null;
            //tail's next will point to null, as it is the last node of the list
            tail.next = null;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            tail.next = newNode;
            //newNode's previous will point to tail
            newNode.previous = tail;
            //newNode will become new tail
            tail = newNode;
            //As it is last node, tail's next will point to null
            tail.next = null;
        }
        //Size will count the number of nodes present in the list
        size++;
    }
    
    //addInMid() will add a node to the middle of the list
    public void addInMid(int data) {
       //Create a new node
        Node newNode = new Node(data);
        
        //If list is empty
        if(head == null) {
            //Both head and tail will point to newNode
            head = tail = newNode;
            //head's previous will point to null
            head.previous = null;
            //tail's next point to null, as it is the last node of the list
            tail.next = null;
        }
        else {
            //current will point to head
            Node current = head, temp = null;
            
            //Store the mid position of the list
            int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);    
            
            //Iterate through list till current points to mid position
            for(int i = 1; i < mid; i++){
                current = current.next;
            }
            
            //Node temp will point to node next to current
            temp = current.next;
            temp.previous = current;
            
            //newNode will be added between current and temp
            current.next = newNode;
            newNode.previous = current;
            newNode.next = temp;
            temp.previous = newNode;
        }
        size++;
    }
    
    //display() will print out the nodes of the list
    public void display() {
        //Node current will point to head
        Node current = head;
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        while(current != null) {
            //Prints each node by incrementing the pointer.

            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        
        InsertMid dList = new InsertMid();
        //Add nodes to the list
        dList.addNode(1);
        dList.addNode(2);
        
        System.out.println("Original list: ");
        dList.display();
        
        //Adding node '3' in the middle
        dList.addInMid(3);
        System.out.println( "Updated List: ");
        dList.display();
        
        //Adding node '4' in the middle
        dList.addInMid(4);
        System.out.println("Updated List: ");
        dList.display();
        
        //Adding node '5' in the middle
        dList.addInMid(5);
        System.out.println("Updated List: ");
        dList.display();
    }
}

输出

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

C#

using System; 
namespace DoublyLinkedList 
{                     
    public class Program
    {
        //Represent a node of the doubly linked list

        public class Node<T>{
            public T data;
            public Node<T> previous;
            public Node<T> next;
            
            public Node(T value) {
                data = value;
            }
        }
        
        public class InsertMid<T>{
            public int size = 0;
            //Represent the head and tail of the doubly linked list
            protected Node<T> head = null;             
             protected Node<T> tail = null;
            
            //addNode() will add a node to the list
            public void addNode(T data) {
                //Create a new node
                Node<T> newNode = new Node<T>(data);
 
                //If list is empty
                if(head == null) {
                    //Both head and tail will point to newNode
                    head = tail = newNode;
                    //head's previous will point to null
                    head.previous = null;
                    //tail's next will point to null, as it is the last node of the list
                    tail.next = null;
                }
                else {
                    //newNode will be added after tail such that tail's next will point to newNode
                    tail.next = newNode;
                    //newNode's previous will point to tail
                    newNode.previous = tail;
                    //newNode will become new tail
                    tail = newNode;
                    //As it is last node, tail's next will point to null
                    tail.next = null;
                }
                //Size will count the number of nodes present in the list
                size++;
            }
    
            //addInMid() will add a node to the middle of the list
            public void addInMid(T data) {//Create a new node
                Node<T> newNode = new Node<T>(data);
 
                //If list is empty
                if(head == null) {
                    //Both head and tail will point to newNode
                    head = tail = newNode;
                    //head's previous will point to null
                    head.previous = null;
                    //tail's next point to null, as it is the last node of the list
                    tail.next = null;
                }
                else {
                    //current will point to head
                    Node<T> current = head, temp = null;
 
                    //Store the mid position of the list
                    int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);    
 
                    //Iterate through list till current points to mid position
                    for(int i = 1; i < mid; i++){
                        current = current.next;
                    }
 
                    //Node temp will point to node next to current
                    temp = current.next;
                    temp.previous = current;
 
                    //newNode will be added between current and temp
                    current.next = newNode;
                    newNode.previous = current;
                    newNode.next = temp;
                    temp.previous = newNode;
                }
                size++;
            }
    
            //display() will print out the nodes of the list
            public void display() {
                //Node current will point to head
                Node<T> current = head;
                if(head == null) {
                    Console.WriteLine("List is empty");
                    return;
                }
                while(current != null) {
                    //Prints each node by incrementing the pointer.

                    Console.Write(current.data + " ");
                    current = current.next;
                }
                Console.WriteLine();
            }
        }
        
        public static void Main()
        {
            InsertMid<int> dList = new InsertMid<int>();
            //Add nodes to the list
            dList.addNode(1);
            dList.addNode(2);
 
            Console.WriteLine("Original list: ");
            dList.display();
 
            //Adding node '3' in the middle
            dList.addInMid(3);
            Console.WriteLine( "Updated List: ");
            dList.display();
 
            //Adding node '4' in the middle
            dList.addInMid(4);
            Console.WriteLine("Updated List: ");
            dList.display();
 
            //Adding node '5' in the middle
            dList.addInMid(5);
            Console.WriteLine("Updated List: ");
            dList.display();
        }    
    }
}

输出

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

PHP

<!DOCTYPE html>
<html>
<body>
<?php
//Represent a node of doubly linked list
class Node{
    public $data;
    public $previous;
    public $next;
    
    function __construct($data){
        $this->data = $data;
    }
}
class InsertMid{
    //Represent the head and tail of the doubly linked list
    public $head;
    public $tail;
    public $size;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
        $this->size = 0;
    }
    
    //addNode() will add a node to the list
    function addNode($data) {
        //Create a new node
        $newNode = new Node($data);
        
        //If list is empty
        if($this->head == NULL) {
            //Both head and tail will point to newNode
            $this->head = $this->tail = $newNode;
            //head's previous will point to NULL
            $this->head->previous = NULL;
            //tail's next will point to NULL, as it is the last node of the list
            $this->tail->next = NULL;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            $this->tail->next = $newNode;
            //newNode's previous will point to tail
            $newNode->previous = $this->tail;
            //newNode will become new tail
            $this->tail = $newNode;
            //As it is last node, tail's next will point to NULL
            $this->tail->next = NULL;
        }
        //Size will count the number of nodes present in the list
        $this->size++;
    }
    
    //addInMid() will add a node to the middle of the list
    function addInMid($data) {
        //Create a new node
        $newNode = new Node($data);
        
        //If list is empty
        if($this->head == NULL) {
            //Both head and tail will point to newNode
            $this->head = $this->tail = $newNode;
            //head's previous will point to NULL
            $this->head->previous = NULL;
            //tail's next point to NULL, as it is the last node of the list
            $this->tail->next = NULL;
        }
        else {
            //current will point to head
            $current = $this->head;
            $temp = NULL;
            
            //Store the mid position of the list
            $mid = ($this->size % 2 == 0) ? ($this->size/2) : (($this->size+1)/2);    
            
            //Iterate through list till current points to mid position
            for($i = 1; $i < $mid; $i++){
                $current = $current->next;
            }
            
            //Node temp will point to node next to current
            $temp = $current->next;
            $temp->previous = $current;
            
            //newNode will be added between current and temp
            $current->next = $newNode;
            $newNode->previous = $current;
            $newNode->next = $temp;
            $temp->previous = $newNode;
        }
        $this->size++;
    }
    
    //display() will print out the nodes of the list
    function display() {
        //Node current will point to head
        $current = $this->head;
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        while($current != NULL) {
            //Prints each node by incrementing pointer.
            print($current->data . " ");
            $current = $current->next;
        }
        print("<br>");
    }
}
    
$dList = new InsertMid();
//Add nodes to the list
$dList->addNode(1);
$dList->addNode(2);
 
print("Original list: <br>");
$dList->display();
 
//Adding node '3' in the middle
$dList->addInMid(3);
print( "Updated List: <br>");
$dList->display();
 
//Adding node '4' in the middle
$dList->addInMid(4);
print("Updated List: <br>");
$dList->display();
 
//Adding node '5' in the middle
$dList->addInMid(5);
print("Updated List: <br>");
$dList->display();
?>
</body>
</html>

输出

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

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问：在双向链表的中间插入新节点的程序。

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问：在双向链表的中间插入新节点的程序。

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