删除链表的第一个节点

给定一个链表，任务是移除链表的第一个节点并更新链表的头指针。
例子：

Input : 1 -> 2 -> 3 -> 4 -> 5 -> NULL
Output : 2 -> 3 -> 4 -> 5 -> NULL

Input : 2 -> 4 -> 6 -> 8 -> 33 -> 67 -> NULL
Output : 4 -> 6 -> 8 -> 33 -> 67 -> NULL

要删除第一个节点，我们需要将第二个节点设为头并删除为第一个节点分配的内存。

C++

// CPP program to remove first node of
// linked list.
#include 
using namespace std;
 
/* Link list node */
struct Node {
    int data;
    struct Node* next;
};
 
/* Function to remove the first node
   of the linked list */
Node* removeFirstNode(struct Node* head)
{
    if (head == NULL)
        return NULL;
 
    // Move the head pointer to the next node
    Node* temp = head;
    head = head->next;
 
    delete temp;
 
    return head;
}
 
// Function to push node at head
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node = new Node;
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 
// Driver code
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
 
    /* Use push() function to construct 
       the below list 8 -> 23 -> 11 -> 29 -> 12 */
    push(&head, 12);
    push(&head, 29);
    push(&head, 11);
    push(&head, 23);
    push(&head, 8);
 
    head = removeFirstNode(head);
    for (Node* temp = head; temp != NULL; temp = temp->next)
        cout << temp->data << " ";
 
    return 0;
}

Java

// Java program to remove first node of
// linked list.
class GFG {
 
    // Link list node /
    static class Node {
        int data;
        Node next;
    };
 
    // Function to remove the first node
    // of the linked list /
    static Node removeFirstNode(Node head)
    {
        if (head == null)
            return null;
 
        // Move the head pointer to the next node
        Node temp = head;
        head = head.next;
 
        return head;
    }
 
    // Function to push node at head
    static Node push(Node head_ref, int new_data)
    {
        Node new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }
 
    // Driver code
    public static void main(String args[])
    {
        // Start with the empty list /
        Node head = null;
 
        // Use push() function to con
        // the below list 8 . 23 . 11 . 29 . 12 /
        head = push(head, 12);
        head = push(head, 29);
        head = push(head, 11);
        head = push(head, 23);
        head = push(head, 8);
 
        head = removeFirstNode(head);
        for (Node temp = head; temp != null; temp = temp.next)
            System.out.print(temp.data + " ");
    }
}
 
// This code is contributed by Arnab Kundu

Python3

# Python3 program to remove first node of 
# linked list.
import sys
 
# Link list node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Function to remove the first node 
# of the linked list
def removeFirstNode(head):
    if not head:
        return None
    temp = head
 
    # Move the head pointer to the next node
    head = head.next
    temp = None
    return head
 
# Function to push node at head
def push(head, data):
    if not head:
        return Node(data)
    temp = Node(data)
    temp.next = head
    head = temp
    return head
 
# Driver code
if __name__=='__main__':
 
    # Start with the empty list
    head = None
 
    # Use push() function to construct  
    # the below list 8 -> 23 -> 11 -> 29 -> 12
    head = push(head, 12)
    head = push(head, 29)
    head = push(head, 11)
    head = push(head, 23)
    head = push(head, 8)
 
    head = removeFirstNode(head)
     
    while(head):
        print("{} ".format(head.data), end ="")
        head = head.next
 
# This code is Contributed by Vikash Kumar 37

C#

// C# program to remove first node of
// linked list.
using System;
 
class GFG
{
 
    // Link list node /
    public class Node
    {
        public int data;
        public Node next;
    };
 
    // Function to remove the first node
    // of the linked list /
    static Node removeFirstNode(Node head)
    {
        if (head == null)
            return null;
 
        // Move the head pointer to the next node
        Node temp = head;
        head = head.next;
 
        return head;
    }
 
    // Function to push node at head
    static Node push(Node head_ref, int new_data)
    {
        Node new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }
 
    // Driver code
    public static void Main(String []args)
    {
        // Start with the empty list /
        Node head = null;
 
        // Use push() function to con
        // the below list 8 . 23 . 11 . 29 . 12 /
        head = push(head, 12);
        head = push(head, 29);
        head = push(head, 11);
        head = push(head, 23);
        head = push(head, 8);
 
        head = removeFirstNode(head);
        for (Node temp = head; temp != null; temp = temp.next)
            Console.Write(temp.data + " ");
    }
}
 
/* This code contributed by PrinciRaj1992 */

Javascript

// javascript program to remove first node of
// linked list.   
// Link list node /
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}
 
    // Function to remove the first node
    // of the linked list /
    function removeFirstNode( head) {
        if (head == null)
            return null;
 
        // Move the head pointer to the next node
         temp = head;
        head = head.next;
 
        return head;
    }
 
    // Function to push node at head
    function push( head_ref , new_data) {
         new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }
 
    // Driver code
     
        // Start with the empty list /
         head = null;
 
        // Use push() function to con
        // the below list 8 . 23 . 11 . 29 . 12 /
        head = push(head, 12);
        head = push(head, 29);
        head = push(head, 11);
        head = push(head, 23);
        head = push(head, 8);
 
        head = removeFirstNode(head);
        for ( temp = head; temp != null; temp = temp.next)
            document.write(temp.data + " ");
 
// This code is contributed by todaysgaurav

输出：

23 11 29 12

时间复杂度： O(1)