Remove last node of the linked list

Given a linked list, the task is to remove the last node of the linked list and update the head pointer of the linked list.

Examples:

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

Explanation: The last node of the linked list
is 5, so 5 is deleted.

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

Explanation: The last node of the linked list
is 67, so 67 is deleted.

Approach: To delete the last node of a linked list, find the second last node and make the next pointer of that node null.

Algorithm:

  1. If the first node is null or there is only one node, then return null
    if headNode == null then return null
    if headNode.nextNode == null then free 
    head and return null
    
  2. Create an extra space secondLast, and traverse the linked list till the second last node.
    while secondLast.nextNode.nextNode != null 
          secondLast = secondLast.nextNode 
    
  3. delete the last node, i.e. the next node of second last node delete(secondLast.nextNode),and set the value of next of second last node to null.

Implementation:

C++



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// CPP program to remove last node of
// linked list.
#include <iostream>
using namespace std;
  
/* Link list node */
struct Node {
    int data;
    struct Node* next;
};
  
/* Function to remove the last node  
   of the linked list */
Node* removeLastNode(struct Node* head)
{
    if (head == NULL)
        return NULL;
  
    if (head->next == NULL) {
        delete head;
        return NULL;
    }
  
    // Find the second last node
    Node* second_last = head;
    while (second_last->next->next != NULL)
        second_last = second_last->next;
  
    // Delete last node
    delete (second_last->next);
  
    // Change next of second last
    second_last->next = NULL;
  
    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 = removeLastNode(head);
    for (Node* temp = head; temp != NULL; temp = temp->next)
        cout << temp->data << " ";
  
    return 0;
}

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Java

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// Java program to remove last node of
// linked list.
class GFG {
  
    // Link list node /
    static class Node {
        int data;
        Node next;
    };
  
    // Function to remove the last node
    // of the linked list /
    static Node removeLastNode(Node head)
    {
        if (head == null)
            return null;
  
        if (head.next == null) {
            return null;
        }
  
        // Find the second last node
        Node second_last = head;
        while (second_last.next.next != null)
            second_last = second_last.next;
  
        // Change next of second last
        second_last.next = null;
  
        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 = removeLastNode(head);
        for (Node temp = head; temp != null; temp = temp.next)
            System.out.print(temp.data + " ");
    }
}
  
// This code is contributed by Arnab Kundu

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Python3

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# Python3 program to remove the last node of 
# linked list.
import sys
import math
  
# Link list node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
  
# 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
  
# Function to remove the last node 
# of the linked list
def removeLastNode(head):
    if head == None:
        return None
    if head.next == None:
        head = None
        return None
    second_last = head
    while(second_last.next.next):
        second_last = second_last.next
    second_last.next = None
    return head
  
# Driver code
if __name__=='__main__':
  
    # Start with the empty list
    head = None
    # 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 = removeLastNode(head)
    while(head):
        print("{} ".format(head.data), end ="")
        head = head.next
  
# This code is contributed by Vikash kumar 37

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C#

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// C# program to remove last node of
// linked list.
using System;
  
class GFG {
  
    // Link list node /
    public class Node {
        public int data;
        public Node next;
    };
  
    // Function to remove the last node
    // of the linked list /
    static Node removeLastNode(Node head)
    {
        if (head == null)
            return null;
  
        if (head.next == null) {
            return null;
        }
  
        // Find the second last node
        Node second_last = head;
        while (second_last.next.next != null)
            second_last = second_last.next;
  
        // Change next of second last
        second_last.next = null;
  
        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 = removeLastNode(head);
        for (Node temp = head; temp != null; temp = temp.next)
            Console.Write(temp.data + " ");
    }
}
  
/* This code contributed by PrinciRaj1992 */

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Output:

8 23 11 29

Complexity Analysis:

  • Time Complexity: O(n).
    The algorithm involves traversal of the linked list till its end, So the time complexity required is O(n).
  • Space Complexity: O(1).
    No extra space is required, so the space complexity is constant

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