Program for n'th node from the end of a Linked List

Given a Linked List and a number n, write a function that returns the value at the n’th node from the end of the Linked List.
For example, if the input is below list and n = 3, then output is “B”

Method 1 (Use length of linked list)
1) Calculate the length of Linked List. Let the length be len.
2) Print the (len – n + 1)th node from the beginning of the Linked List.
Double pointer concept : First pointer is used to store the address of the variable and second pointer used to store the address of the first pointer. If we wish to change the value of a variable by a function, we pass pointer to it. And if we wish to change value of a pointer (i. e., it should start pointing to something else), we pass pointer to a pointer.

Below is the implementation of the above approach:

C++14

// Simple C++ program to find n'th node from end 
#include <bits/stdc++.h> 
using namespace std; 
  
/* Link list node */
struct Node { 
    int data; 
    struct Node* next; 
}; 
  
/* Function to get the nth node from the last of a linked list*/
void printNthFromLast(struct Node* head, int n) 
{ 
    int len = 0, i; 
    struct Node* temp = head; 
  
    // count the number of nodes in Linked List 
    while (temp != NULL) { 
        temp = temp->next; 
        len++; 
    } 
  
    // check if value of n is not 
    // more than length of the linked list 
    if (len < n) 
        return; 
  
    temp = head; 
  
    // get the (len-n+1)th node from the beginning 
    for (i = 1; i < len - n + 1; i++) 
        temp = temp->next; 
  
    cout << temp->data; 
  
    return; 
} 
  
void push(struct Node** head_ref, int new_data) 
{ 
    /* allocate node */
    struct 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; 
} 
  
// Driver Code 
int main() 
{ 
    /* Start with the empty list */
    struct Node* head = NULL; 
  
    // create linked 35->15->4->20 
    push(&head, 20); 
    push(&head, 4); 
    push(&head, 15); 
    push(&head, 35); 
  
    printNthFromLast(head, 4); 
    return 0; 
}

Java

// Simple Java program to find n'th node from end of linked list 
class LinkedList { 
    Node head; // head of the list 
  
    /* Linked List node */
    class Node { 
        int data; 
        Node next; 
        Node(int d) 
        { 
            data = d; 
            next = null; 
        } 
    } 
  
    /* Function to get the nth node from the last of a 
       linked list */
    void printNthFromLast(int n) 
    { 
        int len = 0; 
        Node temp = head; 
  
        // 1) count the number of nodes in Linked List 
        while (temp != null) { 
            temp = temp.next; 
            len++; 
        } 
  
        // check if value of n is not more than length of 
        // the linked list 
        if (len < n) 
            return; 
  
        temp = head; 
  
        // 2) get the (len-n+1)th node from the beginning 
        for (int i = 1; i < len - n + 1; i++) 
            temp = temp.next; 
  
        System.out.println(temp.data); 
    } 
  
    /* 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; 
    } 
  
    /*Driver program to test above methods */
    public static void main(String[] args) 
    { 
        LinkedList llist = new LinkedList(); 
        llist.push(20); 
        llist.push(4); 
        llist.push(15); 
        llist.push(35); 
  
        llist.printNthFromLast(4); 
    } 
} // This code is contributed by Rajat Mishra 

Python3

# Simple Python3 program to find 
# n'th node from end 
class Node: 
    def __init__(self, new_data): 
        self.data = new_data 
        self.next = None
      
class LinkedList: 
    def __init__(self): 
        self.head = None
  
    # createNode and and make linked list 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
  
    # Function to get the nth node from  
    # the last of a linked list  
    def printNthFromLast(self, n): 
        temp = self.head # used temp variable 
          
        length = 0
        while temp is not None: 
            temp = temp.next
            length += 1
          
        # print count  
        if n > length: # if entered location is greater  
                       # than length of linked list 
            print('Location is greater than the' +
                         ' length of LinkedList') 
            return
        temp = self.head 
        for i in range(0, length - n): 
            temp = temp.next
        print(temp.data) 
  
# Driver Code         
llist = LinkedList()  
llist.push(20)  
llist.push(4)  
llist.push(15)  
llist.push(35) 
llist.printNthFromLast(4) 
  
# This code is contributed by Yogesh Joshi 

C#

// C# program to find n'th node from end of linked list  
using System; 
  
public class LinkedList 
{  
    public Node head; // head of the list  
  
    /* Linked List node */
    public class Node  
    {  
        public int data;  
        public Node next;  
        public Node(int d)  
        {  
            data = d;  
            next = null;  
        }  
    }  
  
    /* Function to get the nth node from the last of a  
    linked list */
    void printNthFromLast(int n)  
    {  
        int len = 0;  
        Node temp = head;  
  
        // 1) count the number of nodes in Linked List  
        while (temp != null)  
        {  
            temp = temp.next;  
            len++;  
        }  
  
        // check if value of n is not more than length of  
        // the linked list  
        if (len < n)  
            return;  
  
        temp = head;  
  
        // 2) get the (len-n+1)th node from the beginning  
        for (int i = 1; i < len - n + 1; i++)  
            temp = temp.next;  
  
        Console.WriteLine(temp.data);  
    }  
  
    /* 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;  
    }  
  
    /*Driver code */
    public static void Main(String[] args)  
    {  
        LinkedList llist = new LinkedList();  
        llist.push(20);  
        llist.push(4);  
        llist.push(15);  
        llist.push(35);  
  
        llist.printNthFromLast(4);  
    }  
} 
  
// This code is contributed by Rajput-Ji 

Output

Following is a recursive C code for the same method. Thanks to Anuj Bansal for providing following code.

C

void printNthFromLast(struct Node* head, int n) 
{ 
    static int i = 0; 
    if (head == NULL) 
        return; 
    printNthFromLast(head->next, n); 
    if (++i == n) 
        printf("%d", head->data); 
} 

Time Complexity: O(n) where n is the length of linked list.
Method 2 (Use two pointers)
Maintain two pointers – reference pointer and main pointer. Initialize both reference and main pointers to head. First, move the reference pointer to n nodes from head. Now move both pointers one by one until the reference pointer reaches the end. Now the main pointer will point to nth node from the end. Return the main pointer.
Below image is a dry run of the above approach:

Below is the implementation of the above approach:

C++

// Simple C++ program to  
// find n'th node from end 
#include<bits/stdc++.h> 
using namespace std; 
  
/* Link list node */
struct Node 
{ 
  int data; 
  struct Node* next; 
}; 
  
/* Function to get the nth node  
   from the last of a linked list*/
void printNthFromLast(struct Node *head, int n) 
{ 
  struct Node *main_ptr = head; 
  struct Node *ref_ptr = head; 
  
  int count = 0; 
  if(head != NULL) 
  { 
     while( count < n ) 
     { 
        if(ref_ptr == NULL) 
        { 
           printf("%d is greater than the no. of "
                    "nodes in list", n); 
           return; 
        } 
        ref_ptr = ref_ptr->next; 
        count++; 
     } /* End of while*/
      
     if(ref_ptr == NULL) 
     { 
        head = head->next; 
        if(head != NULL) 
            printf("Node no. %d from last is %d ", n, main_ptr->data); 
     } 
     else
     { 
       while(ref_ptr != NULL) 
       { 
          main_ptr = main_ptr->next; 
          ref_ptr  = ref_ptr->next; 
       } 
       printf("Node no. %d from last is %d ", n, main_ptr->data); 
     } 
  } 
} 
  
// Function to push 
void push(struct Node** head_ref, int new_data) 
{ 
  /* allocate node */
  struct 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; 
} 
  
/* Driver program to test above function*/
int main() 
{ 
  /* Start with the empty list */
  struct Node* head = NULL; 
  push(&head, 20); 
  push(&head, 4); 
  push(&head, 15); 
  push(&head, 35); 
  
  printNthFromLast(head, 4); 
}

Java

// Java program to find n'th  
// node from end using slow and 
// fast pointers 
class LinkedList  
{ 
    Node head; // head of the list 
  
    /* Linked List node */
    class Node { 
        int data; 
        Node next; 
        Node(int d) 
        { 
            data = d; 
            next = null; 
        } 
    } 
  
    /* Function to get the  
      nth node from end of list */
    void printNthFromLast(int n) 
    { 
        Node main_ptr = head; 
        Node ref_ptr = head; 
  
        int count = 0; 
        if (head != null)  
        { 
            while (count < n)  
            { 
                if (ref_ptr == null)  
                { 
                    System.out.println(n  
                     + " is greater than the no "
                       + " of nodes in the list"); 
                    return; 
                } 
                ref_ptr = ref_ptr.next; 
                count++; 
            } 
  
            if(ref_ptr == null) 
            { 
              head = head.next; 
              if(head != null) 
                System.out.println("Node no. " + n + 
                                   " from last is " +  
                                      head.data); 
            } 
            else
            { 
                    
              while (ref_ptr != null)  
              { 
                  main_ptr = main_ptr.next; 
                  ref_ptr = ref_ptr.next; 
              } 
              System.out.println("Node no. " + n + 
                                " from last is " + 
                                  main_ptr.data); 
            } 
        } 
    } 
  
    /* 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; 
    } 
  
    /*Driver program to test above methods */
    public static void main(String[] args) 
    { 
        LinkedList llist = new LinkedList(); 
        llist.push(20); 
        llist.push(4); 
        llist.push(15); 
        llist.push(35); 
  
        llist.printNthFromLast(4); 
    } 
}  
// This code is contributed by Rajat Mishra 

Python

# Python program to find n'th node from end using slow 
# and fast pointer 
  
# Node class  
class Node: 
  
    # Constructor to initialize the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
class LinkedList: 
  
    # Function to initialize head 
    def __init__(self): 
        self.head = None
  
    # Function to insert a new node at the beginning 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
  
    def printNthFromLast(self, n): 
        main_ptr = self.head 
        ref_ptr = self.head  
      
        count = 0 
        if(self.head is not None): 
            while(count < n ): 
                if(ref_ptr is None): 
                    print "% d is greater than the  
                           no. pf nodes in list" %(n) 
                    return
   
                ref_ptr = ref_ptr.next
                count += 1
      
        if(ref_ptr is None): 
            self.head = self.head.next
            if(self.head is not None): 
                 print "Node no. % d from last is % d " 
                                   %(n, main_ptr.data) 
        else: 
            
  
          while(ref_ptr is not None): 
              main_ptr = main_ptr.next 
              ref_ptr = ref_ptr.next
  
          print "Node no. % d from last is % d " 
                                     %(n, main_ptr.data) 
  
  
# Driver program to test above function 
llist = LinkedList() 
llist.push(20) 
llist.push(4) 
llist.push(15) 
llist.push(35) 
  
llist.printNthFromLast(4) 
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007) 

C#

// C# program to find n'th node from end using slow and 
// fast pointerspublic  
using System; 
  
public class LinkedList 
{ 
  Node head; // head of the list 
  
  /* Linked List node */
  public class Node  
  { 
    public int data; 
    public Node next; 
    public Node(int d) 
    { 
      data = d; 
      next = null; 
    } 
  } 
  
  /* Function to get the nth node from end of list */
  void printNthFromLast(int n) 
  { 
    Node main_ptr = head; 
    Node ref_ptr = head; 
  
    int count = 0; 
    if (head != null) 
    { 
      while (count < n)  
      { 
        if (ref_ptr == null) 
        { 
          Console.WriteLine(n + " is greater than the no "
                            + " of nodes in the list"); 
          return; 
        } 
        ref_ptr = ref_ptr.next; 
        count++; 
      } 
  
      if(ref_ptr == null) 
      { 
        head = head.next; 
        if(head != null) 
          Console.WriteLine("Node no. " +  
                            n + " from last is " + 
                            main_ptr.data); 
      } 
      else
      { 
        while (ref_ptr != null) 
        { 
          main_ptr = main_ptr.next; 
          ref_ptr = ref_ptr.next; 
        } 
        Console.WriteLine("Node no. " +  
                          n + " from last is " + 
                          main_ptr.data); 
      } 
    } 
  } 
  
  /* 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; 
  } 
  
  /*Driver code */
  public static void Main(String[] args) 
  { 
    LinkedList llist = new LinkedList(); 
    llist.push(20); 
    llist.push(4); 
    llist.push(15); 
    llist.push(35); 
  
    llist.printNthFromLast(4); 
  } 
} 
  
/* This code is contributed by PrinciRaj1992 */

Output

Node no. 4 from last is 35

Time Complexity: O(n) where n is the length of linked list.
Please write comments if you find the above codes/algorithms incorrect, or find other ways to solve the same problem.

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My Personal Notes

Program for n’th node from the end of a Linked List

C++14

Java

Python3

C#

C

C++

Java

Python

C#

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