Print the last k nodes of the linked list in reverse order | Recursive approach

Given a linked list containing N nodes and a positive integer k should be less than or equal to N. The task is to print the last k nodes of the list in reverse order.

Examples:

Input: list: 1->2->3->4->5, k = 2                       
Output: 5 4

Input: list: 3->10->6->9->12->2->8, k = 4 
Output: 8 2 12 9

Source: Amazon Interview Experience SDE Off Campus.

Recursive Approach: Recursively traverse the linked list. When returning from each recursive call keep track of the node number, considering the last node as number 1, second last as number 2 and so on. This counting could be tracked with the help of a global or pointer variable. With the help of this count variable, print the nodes having a node number less than or equal to k.

Below is the implementation of the above approach: 

C++

// C++ implementation to print the last k nodes
// of linked list in reverse order
#include <bits/stdc++.h>
using namespace std;

// Structure of a node
struct Node {
    int data;
    Node* next;
};

// Function to get a new node
Node* getNode(int data)
{
    // allocate space
    Node* newNode = new Node;

    // put in data
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}

// Function to print the last k nodes
// of linked list in reverse order
void printLastKRev(Node* head,
                     int& count, int k)
{
    // if list is empty
    if (!head)
        return;

    // Recursive call with the next node
    // of the list
    printLastKRev(head->next, count, k);

    // Count variable to keep track of
    // the last k nodes
    count++;

    // Print data
    if (count <= k)
        cout << head->data << " ";
}

// Driver code
int main()
{
    // Create list: 1->2->3->4->5
    Node* head = getNode(1);
    head->next = getNode(2);
    head->next->next = getNode(3);
    head->next->next->next = getNode(4);
    head->next->next->next->next = getNode(5);

    int k = 4, count = 0;

    // print the last k nodes
    printLastKRev(head, count, k);

    return 0;
}

Java

// Java implementation to print the last k nodes
// of linked list in reverse order
class GfG
{

// Structure of a node
static class Node
{
    int data;
    Node next;
}

// Function to get a new node
static Node getNode(int data)
{
    // allocate space
    Node newNode = new Node();

    // put in data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}

static class C
{
    int count = 0;
}

// Function to print the last k nodes
// of linked list in reverse order
static void printLastKRev(Node head, C c, int k)
{
    // if list is empty
    if (head == null)
        return;

    // Recursive call with the next node
    // of the list
    printLastKRev(head.next, c, k);

    // Count variable to keep track of
    // the last k nodes
    c.count++;

    // Print data
    if (c.count <= k)
        System.out.print(head.data + " ");
}

// Driver code
public static void main(String[] args)
{
    // Create list: 1->2->3->4->5
    Node head = getNode(1);
    head.next = getNode(2);
    head.next.next = getNode(3);
    head.next.next.next = getNode(4);
    head.next.next.next.next = getNode(5);

    int k = 4;
    C c = new C();

    // print the last k nodes
    printLastKRev(head, c, k);
}
}

// This code is contributed by prerna saini

Python

# Python implementation to print the last k nodes
# of linked list in reverse order

# Node class
class Node:

    # Function to initialise the node object
    def __init__(self, data):
        self.data = data # Assign data
        self.next =None

# Function to get a new node
def getNode(data):

    # allocate space
    newNode = Node(0)

    # put in data
    newNode.data = data
    newNode.next = None
    return newNode

class C:
    def __init__(self, data):
        self.count = data

# Function to print the last k nodes
# of linked list in reverse order
def printLastKRev(head, c, k):

    # if list is empty
    if (head == None):
        return

    # Recursive call with the next node
    # of the list
    printLastKRev(head.next, c, k)

    # Count variable to keep track of
    # the last k nodes
    c.count = c.count + 1

    # Print data
    if (c.count <= k) :
        print(head.data, end = " ")

# Driver code

# Create list: 1->2->3->4->5
head = getNode(1)
head.next = getNode(2)
head.next.next = getNode(3)
head.next.next.next = getNode(4)
head.next.next.next.next = getNode(5)

k = 4
c = C(0)

# print the last k nodes
printLastKRev(head, c, k)

# This code is contributed by Arnab Kundu

C#

// C# implementation to print the last k
// nodes of linked list in reverse order
using System;

class GFG
{

// Structure of a node
public class Node
{
    public int data;
    public Node next;
}

// Function to get a new node
static Node getNode(int data)
{
    // allocate space
    Node newNode = new Node();

    // put in data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}

public class C
{
    public int count = 0;
}

// Function to print the last k nodes
// of linked list in reverse order
static void printLastKRev(Node head, C c, int k)
{
    // if list is empty
    if (head == null)
        return;

    // Recursive call with the next
    // node of the list
    printLastKRev(head.next, c, k);

    // Count variable to keep track
    // of the last k nodes
    c.count++;

    // Print data
    if (c.count <= k)
        Console.Write(head.data + " ");
}

// Driver code
public static void Main(String []args)
{

    // Create list: 1->2->3->4->5
    Node head = getNode(1);
    head.next = getNode(2);
    head.next.next = getNode(3);
    head.next.next.next = getNode(4);
    head.next.next.next.next = getNode(5);

    int k = 4;
    C c = new C();

    // print the last k nodes
    printLastKRev(head, c, k);
}
}

// This code is contributed by Arnab Kundu

Javascript

<script>

// Javascript implementation of the approach

// Structure of a node
class Node {
        constructor() {
                this.data = 0;
                this.next = null;
             }
        }


// Function to get a new node
function getNode( data)
{
    // allocate space
    var newNode = new Node();

    // put in data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}

 class C
{
constructor() {
    this.count = 0;
    }
}

// Function to print the last k nodes
// of linked list in reverse order
function printLastKRev( head,  c,  k)
{
    // if list is empty
    if (head == null)
        return;

    // Recursive call with the next node
    // of the list
    printLastKRev(head.next, c, k);

    // Count variable to keep track of
    // the last k nodes
    c.count++;

    // Print data
    if (c.count <= k)
        document.write(head.data + " ");
}

// Driver Code

// Create list: 1->2->3->4->5
var head = getNode(1);
head.next = getNode(2);
head.next.next = getNode(3);
head.next.next.next = getNode(4);
head.next.next.next.next = getNode(5);

let k = 4;
let c = new C();

// print the last k nodes
printLastKRev(head, c, k);

// This code is contributed by jana_sayantan.
</script>

Output

5 4 3 2 

Time Complexity: O(n).

Iterative Approach: The idea is to use Stack Data Structure. 

1. Push all linked list nodes to a stack.
2. Pop k nodes from the stack and print them.

Time Complexity: O(n).

Two Pointer Approach The idea is similar to find k-th node from end of linked list. 

1. Move first pointer k nodes ahead.
2. Now start another pointer, second from head.
3. When first pointer reaches end, second pointer points to k-th node.
4. Finally using the second pointer, print last k nodes.

Time Complexity: O(n).