删除链表的备用节点

给定一个单链表，从第二个节点开始删除它的所有备用节点。例如，如果给定的链表是 1->2->3->4->5 那么你的函数应该将它转换为 1->3->5，如果给定的链表是 1->2-> 3->4 然后将其转换为 1->3。

方法一（迭代）
跟踪要删除的节点的前一个。首先，改变上一个节点的下一个链接，然后释放为该节点分配的内存。

C++

// C++ program to remove alternate
// nodes of a linked list
#include 
using namespace std;
 
/* A linked list node */
class Node
{
    public:
    int data;
    Node *next;
};
 
/* deletes alternate nodes
of a list starting with head */
void deleteAlt(Node *head)
{
    if (head == NULL)
        return;
 
    /* Initialize prev and node to be deleted */
    Node *prev = head;
    Node *node = head->next;
 
    while (prev != NULL && node != NULL)
    {
        /* Change next link of previous node */
        prev->next = node->next;
 
        /* Free memory */
        free(node);
 
        /* Update prev and node */
        prev = prev->next;
        if (prev != NULL)
            node = prev->next;
    }
}
 
/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(Node** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node = new Node();
 
    /* put in the data */
    new_node->data = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
 
/* Function to print nodes in a given linked list */
void printList(Node *node)
{
    while (node != NULL)
    {
        cout<< node->data<<" ";
        node = node->next;
    }
}
 
/* Driver code */
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
 
    /* Using push() to construct below list
    1->2->3->4->5 */
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);
 
    cout<<"List before calling deleteAlt() \n";
    printList(head);
 
    deleteAlt(head);
 
    cout<<"\nList after calling deleteAlt() \n";
    printList(head);
 
    return 0;
}
 
// This code is contributed by rathbhupendra

C

// C program to remove alternate nodes of a linked list
#include
#include
 
/* A linked list node */
struct Node
{
    int data;
    struct Node *next;
};
 
/* deletes alternate nodes of a list starting with head */
void deleteAlt(struct Node *head)
{
    if (head == NULL)
        return;
 
    /* Initialize prev and node to be deleted */
    struct Node *prev = head;
    struct Node *node = head->next;
 
    while (prev != NULL && node != NULL)
    {
        /* Change next link of previous node */
        prev->next = node->next;
 
        /* Free memory */
        free(node);
 
        /* Update prev and node */
        prev = prev->next;
        if (prev != NULL)
            node = prev->next;
    }
}
 
/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */
/* Given a reference (pointer to pointer) to the head
  of a list and an int, push a new node on the front
  of the list. */
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node =
        (struct Node*) malloc(sizeof(struct Node));
 
    /* put in the data  */
    new_node->data  = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref)    = new_node;
}
 
/* Function to print nodes in a given linked list */
void printList(struct Node *node)
{
    while (node != NULL)
    {
        printf("%d ", node->data);
        node = node->next;
    }
}
 
/* Driver program to test above functions */
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
 
    /* Using push() to construct below list
      1->2->3->4->5  */
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);
 
    printf("\nList before calling deleteAlt() \n");
    printList(head);
 
    deleteAlt(head);
 
    printf("\nList after calling deleteAlt() \n");
    printList(head);
 
    return 0;
}

Java

// Java program to delete alternate nodes of a linked list
class LinkedList
{
    Node head;  // head of list
  
    /* Linked list Node*/
    class Node
    {
        int data;
        Node next;
        Node(int d) {data = d; next = null; }
    }
 
    void deleteAlt()
    {
       if (head == null)
          return;
 
       Node prev = head;
       Node now = head.next;
 
       while (prev != null && now != null)
       {          
           /* Change next link of previous node */
           prev.next = now.next;
 
           /* Free node */
           now = null;
 
           /*Update prev and now */
           prev = prev.next;
           if (prev != null)
              now = prev.next;
       }
    }                
 
                     
    /* Utility functions */
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);
  
        /* 3. Make next of new Node as head */
        new_node.next = head;
  
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Function to print linked list */
    void printList()
    {
        Node temp = head;
        while(temp != null)
        {
           System.out.print(temp.data+" ");
           temp = temp.next;
        } 
        System.out.println();
    }
 
     /* Driver program to test above functions */
    public static void main(String args[])
    {
        LinkedList llist = new LinkedList();
         
        /* Constructed Linked List is 1->2->3->4->5->null */
        llist.push(5);
        llist.push(4);
        llist.push(3);
        llist.push(2);
        llist.push(1);
         
        System.out.println("Linked List before calling deleteAlt() ");
        llist.printList();
         
        llist.deleteAlt();
         
        System.out.println("Linked List after calling deleteAlt() ");
        llist.printList();
    }
}
/* This code is contributed by Rajat Mishra */

Python3

# Python3 program to remove alternate
# nodes of a linked list
import math
 
# A linked list node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
         
# deletes alternate nodes
# of a list starting with head
def deleteAlt(head):
    if (head == None):
        return
 
    # Initialize prev and node to be deleted
    prev = head
    now = head.next
 
    while (prev != None and now != None):
         
        # Change next link of previous node
        prev.next = now.next
 
        # Free memory
        now = None
 
        # Update prev and node
        prev = prev.next
        if (prev != None):
            now = prev.next
     
# UTILITY FUNCTIONS TO TEST fun1() and fun2()
# Given a reference (pointer to pointer) to the head
# of a list and an , push a new node on the front
# of the list.
def push(head_ref, new_data):
     
    # allocate node
    new_node = Node(new_data)
 
    # put in the data
    new_node.data = new_data
 
    # link the old list off the new node
    new_node.next = head_ref
 
    # move the head to po to the new node
    head_ref = new_node
    return head_ref
 
# Function to print nodes in a given linked list
def prList(node):
    while (node != None):
        print(node.data, end = " ")
        node = node.next
     
# Driver code
if __name__=='__main__':
     
    # Start with the empty list
    head = None
 
    # Using head=push() to construct below list
    # 1.2.3.4.5
    head = push(head, 5)
    head = push(head, 4)
    head = push(head, 3)
    head = push(head, 2)
    head = push(head, 1)
 
    print("List before calling deleteAlt() ")
    prList(head)
 
    deleteAlt(head)
 
    print("\nList after calling deleteAlt() ")
    prList(head)
 
# This code is contributed by Srathore

C#

// C# program to delete alternate
// nodes of a linked list
using System;
 
public class LinkedList
{
    Node head; // head of list
 
    /* Linked list Node*/
    public class Node
    {
        public int data;
        public Node next;
        public Node(int d)
        {
            data = d; next = null;
             
        }
    }
 
    void deleteAlt()
    {
        if (head == null)
            return;
 
        Node prev = head;
        Node now = head.next;
 
        while (prev != null && now != null)
        {        
            /* Change next link of previous node */
            prev.next = now.next;
 
            /* Free node */
            now = null;
 
            /*Update prev and now */
            prev = prev.next;
            if (prev != null)
                now = prev.next;
        }
    }                
 
                     
    /* Utility functions */
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Function to print linked list */
    void printList()
    {
        Node temp = head;
        while(temp != null)
        {
        Console.Write(temp.data+" ");
        temp = temp.next;
        }
        Console.WriteLine();
    }
 
    /* Driver code*/
    public static void Main(String []args)
    {
        LinkedList llist = new LinkedList();
         
        /* Constructed Linked List is
        1->2->3->4->5->null */
        llist.push(5);
        llist.push(4);
        llist.push(3);
        llist.push(2);
        llist.push(1);
         
        Console.WriteLine("Linked List before" +
                            "calling deleteAlt() ");
        llist.printList();
         
        llist.deleteAlt();
         
        Console.WriteLine("Linked List after" +
                            "calling deleteAlt() ");
        llist.printList();
    }
}
 
// This code has been contributed
// by 29AjayKumar

Javascript

 
// Javascript program to delete alternate
// nodes of a linked list
var head; // head of list
 
    /* Linked list Node */
     class Node {
            constructor(val) {
                this.data = val;
                this.next = null;
            }
        }
      
    function deleteAlt() {
        if (head == null)
            return;
 
        var prev = head;
        var now = head.next;
 
        while (prev != null && now != null) {
            /* Change next link of previous node */
            prev.next = now.next;
 
            /* Free node */
            now = null;
 
            /* Update prev and now */
            prev = prev.next;
            if (prev != null)
                now = prev.next;
        }
    }
 
    /* Utility functions */
 
    /* Inserts a new Node at front of the list. */
    function push(new_data) {
        /*
         * 1 & 2: Allocate the Node & Put in the data
         */
        var new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Function to print linked list */
    function printList() {
        var temp = head;
        while (temp != null) {
            document.write(temp.data + " ");
            temp = temp.next;
        }
        document.write("<br/>");
    }
 
    /* Driver program to test above functions */
 
 
        /* Constructed Linked List is
        1->2->3->4->5->null */
        push(5);
        push(4);
        push(3);
        push(2);
        push(1);
 
        document.write(
        "Linked List before calling deleteAlt() <br/>"
        );
        printList();
 
        deleteAlt();
 
        document.write(
        "Linked List after calling deleteAlt()<br/> "
        );
        printList();
 
// This code contributed by gauravrajput1
 

输出：

List before calling deleteAlt() 
1 2 3 4 5 
List after calling deleteAlt() 
1 3 5 

时间复杂度： O(n)，其中 n 是给定链表中的节点数。
方法 2（递归）
递归代码使用与方法 1 相同的方法。递归代码简单而简短，但会导致对大小为 n 的链表的 O(n) 递归函数调用。

C++

/* deletes alternate nodes of a list starting with head */
void deleteAlt(Node *head)
{
    if (head == NULL)
        return;
 
    Node *node = head->next;
 
    if (node == NULL)
        return;
 
    /* Change the next link of head */
    head->next = node->next;
 
    /* free memory allocated for node */
    free(node);
 
    /* Recursively call for the new next of head */
    deleteAlt(head->next);
}
 
// This code is contributed by rathbhupendra

C

/* deletes alternate nodes of a list starting with head */
void deleteAlt(struct Node *head)
{
    if (head == NULL)
        return;
 
    struct Node *node = head->next;
 
    if (node == NULL)
        return;
 
    /* Change the next link of head */
    head->next = node->next;
 
    /* free memory allocated for node */
    free(node);
 
    /* Recursively call for the new next of head */
    deleteAlt(head->next);
}

Java

/* deletes alternate nodes of a list
starting with head */
static Node deleteAlt(Node head)
{
    if (head == null)
        return;
 
    Node node = head.next;
 
    if (node == null)
        return;
 
    /* Change the next link of head */
    head.next = node.next;
 
 
    /* Recursively call for the new next of head */
    head.next = deleteAlt(head.next);
}
 
// This code is contributed by Arnab Kundu

蟒蛇3

# deletes alternate nodes of a list starting with head
def deleteAlt(head):
    if (head == None):
        return
 
    node = head.next
 
    if (node == None):
        return
 
    # Change the next link of head
    head.next = node.next
 
    # free memory allocated for node
    #free(node)
 
    # Recursively call for the new next of head
    deleteAlt(head.next)
 
# This code is contributed by Srathore

C＃

/* deletes alternate nodes of a list
starting with head */
static Node deleteAlt(Node head)
{
    if (head == null)
        return;
 
    Node node = head.next;
 
    if (node == null)
        return;
 
    /* Change the next link of head */
    head.next = node.next;
 
 
    /* Recursively call for the new next of head */
    head.next = deleteAlt(head.next);
}
 
// This code is contributed by Arnab Kundu

Javascript

/* deletes alternate nodes of a list
starting with head */
function deleteAlt(head)
{
    if (head == null)
        return;
 
    var node = head.next;
 
    if (node == null)
        return;
 
    /* Change the next link of head */
    head.next = node.next;    /* Recursively call for the new next of head */
    head.next = deleteAlt(head.next);
}
 
 
// This code contributed by aashish1995

时间复杂度： O(n)

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