Find the second last node of a linked list

Find out second last node of given singly linked list. We can solve this problem using single traversal of linked list. Before write actual algorithm consider following test cases.

Test Case 1) : When linked list are empty then show valid message.

2) When linked list are contain less than two nodes then display the (Only one node in this linked list).

3) Find the second last node in single traversal.

Suppose we are inserted the following (6, 3, 2, 7, 1, 9 ) node in a sequence.

Find the second last node of a linked list

Here given code implementation process.

//C Program
//Find the second last node of a linked list
#include<stdio.h>
#include <stdlib.h> //for malloc function

//create structure
struct Node{
  int data;
  struct Node*next;
};
//function prototype
void insert(struct Node**,int);
void display(struct Node*);
void second_last(struct Node*);
//insert Node element
void insert(struct Node**head,int value){
  //Create dynamic node
  struct Node*node=(struct Node*)malloc(sizeof(struct Node));
  if(node==NULL){
    printf("Memory overflow\n");
  }else{
    node->data=value;
    node->next=NULL;
    if(*head==NULL){
      *head=node;
    }else{
      struct Node*temp=*head;
      //find last node
      while(temp->next!=NULL){
        temp=temp->next;
      }
      //add node at last possition
      temp->next=node;
    }
  }
}
//Find the second last node of a linked list
void second_last(struct Node*temp){
  if(temp==NULL){
    printf("Empty linked list");
  }else if(temp->next==NULL){
    printf("Only one node in this linked list");
  }else{
    //find second last node
    while(temp!=NULL && temp->next!=NULL && temp->next->next!=NULL){
      temp=temp->next->next;
    }
    printf("\nSecond last element : %d\n",temp->data );
  }
}
//Display element of Node
void display(struct Node*temp){
  
  if(temp==NULL){
    printf("Empty linked list");
  }
  while(temp!=NULL){
    printf("%d  ",temp->data);
    temp=temp->next;
  }
}
int main(){
  //create node pointer
  struct Node*head=NULL;
  //insert element of linked list

  insert(&head,6);
  insert(&head,3);
  insert(&head,2);
  insert(&head,7);
  insert(&head,1);
  insert(&head,9);
  //display all node
  display(head);
  second_last(head);
}

Output

6  3  2  7  1  9  
Second last element : 1
//C++ Program 
//Find the second last node of a linked list
#include<iostream>
using namespace std;

//create structure
struct Node{
  int data;
  struct Node*next;
};
class LinkedList{
  Node*head;//head node
  public:
    LinkedList();
    void insert(int);
    void display();
    void second_last();
};
LinkedList::LinkedList(){
  head=NULL;
}
//insert node at end of linked list
void LinkedList::insert(int value){
    //Create dynamic node
  struct Node*node=new Node;
  if(node==NULL){
    cout<<"Memory overflow\n";
  }else{
    node->data=value;
    node->next=NULL;
    if(head==NULL){
      //base condition
      head=node;
    }else{
      Node*temp=head;
      while(temp->next!=NULL){
        temp=temp->next;
      }
      //add newly node at last
      temp->next=node;
    }
  }
}
//display all node value in linked list
void LinkedList:: display(){
  if(head==NULL){
    cout<<"Empty linked list";
  }
  else{
    Node*temp=head;
    cout<<"Linked List : ";
    while(temp!=NULL){
      //print node value
      cout<<temp->data<<" ";
      temp=temp->next;
    }
  }

}
//Find the second last node of a linked list
void LinkedList:: second_last(){
  struct Node*temp=head;
  if(temp==NULL){
    cout<<"Empty linked list"<<endl;
  }else if(temp->next==NULL){
    cout<<"Only one node in this linked list"<<endl;
  }else{
    //find second last node
    while(temp!=NULL && temp->next!=NULL && temp->next->next!=NULL){
      temp=temp->next->next;
    }
    cout<<"\nSecond last element : "<<temp->data <<endl;
  }
}
int main(){
 
  //create object
  LinkedList obj;
  //insert element of linked list
  obj.insert(6);
  obj.insert(3);
  obj.insert(2);
  obj.insert(7);
  obj.insert(1);
  obj.insert(9);

  //display all node
  obj.display();

  obj.second_last();
  return 0;
}

Output

Linked List : 6 3 2 7 1 9 
Second last element : 1
//Java Program
//Find the second last node of a linked list
class Node {
  public int data;
  public Node next;
  public Node(int value) {
    data = value;
    next = null;
  }
}

public class LinkedList {

  public Node head;
  //Class constructors
  LinkedList() {
    head = null;
  }
  //insert element
  public void insert(int value) {
    //Create  node
    Node node = new Node(value);

    if (head == null) head = node;
    else {
      Node temp = head;
      //find last node
      while (temp.next != null) {
        temp = temp.next;
      }
      temp.next = node;
    }

  }
  //Display all Linked List elements
  public void display() {
    if (head != null) {
      System.out.print("Linked List Element :");
      Node temp = head;
      while (temp != null) {
        System.out.print("  " + temp.data);
        temp = temp.next;
      }
    } else {
      System.out.println("Empty Linked list");
    }
  }
  //Find the second last node of a linked list
  public void secondLast() {
    Node temp = head;
    if (temp == null) {
      System.out.print("Empty linked list");
    } else if (temp.next == null) {
      System.out.print("Only one node in this linked list");
    } else {
      //find second last node
      while (temp != null && temp.next != null && temp.next.next != null) {
        temp = temp.next.next;
      }
      System.out.print("\nSecond last element : " + temp.data);
    }
  }

  public static void main(String[] args) {

    LinkedList obj = new LinkedList();
    //insert element of linked list
    obj.insert(6);
    obj.insert(3);
    obj.insert(2);
    obj.insert(7);
    obj.insert(1);
    obj.insert(9);

    //display all node
    obj.display();

    obj.secondLast();
  }
}

Output

Linked List Element :  6  3  2  7  1  9
Second last element : 1
#Python Program
#Find the second last node of a linked list
class Node:
    def __init__(self,data):
        self.data=data
        self.next=None

#Create Class Linked    
class Linked:
    def __init__(self):
        #Assign default value
        self.head=None

    #insert new node to linked list  
    def insert(self,data):
        node=Node(data)
        node.next=None
        if self.head==None:
            self.head=node
        else:
            temp=self.head
            while temp.next!=None:
                temp=temp.next
            #add node    
            temp.next=node

    def display(self):
        if(self.head==None):
            print("Empty Linked List")
            return

        temp=self.head
        print("Linked List Elements : ")
        while(temp!=None):
          print(temp.data,end=" ")
          temp=temp.next
    def secondLast(self):
        temp=self.head
        if(temp==None):
          print("Empty linked list")
        elif (temp.next==None):
          print("Only one node in this linked list")
        else:
          #find second last node
          while(temp!=None and temp.next!=None and temp.next.next!=None):
            temp=temp.next.next
          
          print("\nSecond last element : ",temp.data)
        
      

def main():
    #Create Object of class Linked
    obj=Linked()
    #insert linked list node
    obj.insert(6)
    obj.insert(3)
    obj.insert(2)
    obj.insert(7)
    obj.insert(1)
    obj.insert(9)

    #display all node
    obj.display()

    obj.secondLast()

if __name__=="__main__":
    main()

Output

Linked List Elements : 
6 3 2 7 1 9 
Second last element :  1
//C# Program
//Find the second last node of a linked list
using System;
//node class
public class Node{
   public  int data;
   public  Node next;
}
class Program
{
    Node head;
    public Program(){
        head=null;
    }
    //insert node of linked list
    public void insert(int data){
        Node newNode=new Node();
        newNode.data=data;
        newNode.next=null;
        if(head==null) head=newNode;
        else{
            Node temp=head;
            //get last node
            while(temp.next!=null){
                temp=temp.next;
            }
            //add new node
            temp.next=newNode;
        }
    }
    //display linked list nodes value
    public void display(){
        if(head==null){
            Console.Write("Empty List");
        }else{
            Node temp=head;
            while(temp!=null){
                Console.Write("  {0}",temp.data);
                temp=temp.next;
            }
            
        }
    }
    //Find the second last node of a linked list
    public void  secondLast(){
      Node temp=head;
      if(temp==null){
        Console.WriteLine("Empty linked list");
      }else if(temp.next==null){
        Console.WriteLine("Only one node in this linked list");
      }else{
        //find second last node
        while(temp!=null && temp.next!=null && temp.next.next!=null){
          temp=temp.next.next;
        }
        Console.WriteLine("\nSecond last element : "+temp.data);
      }
    }
    static void Main()
    {
        Program obj=new Program();
        //insert element of linked list
        obj.insert(6);
        obj.insert(3);
        obj.insert(2);
        obj.insert(7);
        obj.insert(1);
        obj.insert(9);

        //display all node
        obj.display();

        obj.secondLast();
    }
}

Output

6 3 2 7 1 9
Second last element : 1
<?php
//Php program 
//Find the second last node of a linked list
class Node
{
    public $data;
    public $next;
    function __construct($data)
    {
        $this->data = $data;
        $this->next = NULL;
    }
}
class LinkedList{

    private $head;
    function __construct()
    {
        $head=NULL;
    }
    /*
    * Append the Given data value at end of linked list
    * Fun : insert
    * Parm: data value
    *@return None
    */
    function insert($data)
    {
        $newNode=new Node($data); 
        if($this->head==NULL)
        {
            $this->head=$newNode;
        }else{
            $temp=$this->head;
            //find last node of linked list
            while($temp->next!=NULL){
                $temp=$temp->next;
            }
            //add new node to last of linked list
            $temp->next=$newNode;
        }
    }
    //Display all inserted node in linked list
    function display()
    {
        if($this->head==NULL)
        {
            echo "Empty Linked List";
        }
        else{
            $temp=$this->head;
            echo "Linked List :";
            while($temp!=NULL){
                //display node value
                echo "  ".$temp->data;
                $temp=$temp->next; //visit to next node
            }
        }   
    }
    //Find the second last node of a linked list
    function second_last()
    {
      $temp=$this->head;
      if($temp==NULL)
      {
        echo "Empty linked list";
      }else if($temp->next==NULL)
      {
        echo "Only one node in this linked list";
      }else
      {
        //find second last node
        while($temp!=NULL && $temp->next!=NULL && $temp->next->next!=NULL)
        {
          $temp=$temp->next->next;
        }
        echo "<br>Second last element : ".$temp->data;
      }
    }

}
function main(){
  //Make a object of LinkedList class
  $obj= new LinkedList();

  /*
  *Insert following nodes in linked list
  */
  $obj->insert(6);
  $obj->insert(3);
  $obj->insert(2);
  $obj->insert(7);
  $obj->insert(1);
  $obj->insert(9);
  $obj->display();
  $obj->second_last();
}
main();
?>

Output

Linked List : 6 3 2 7 1 9
Second last element : 1

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