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Print alternate nodes of a linked list using recursion

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  • Difficulty Level : Basic
  • Last Updated : 17 Feb, 2022

Given a linked list, print alternate nodes of this linked list.
Examples : 
 

Input : 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9 -> 10
Output : 1 -> 3 -> 5 -> 7 -> 9 

Input : 10 -> 9
Output : 10

 

Recursive Approach : 
1. Initialize a static variable(say flag) 
2. If flag is odd print the node 
3. increase head and flag by 1, and recurse for next nodes.
 

C++




// CPP code to print alternate nodes
// of a linked list using recursion
#include <bits/stdc++.h>
using namespace std;
 
// A linked list node
struct Node {
    int data;
    struct Node* next;
};
 
// Inserting node at the beginning
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node =
       (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 
// Function to print alternate nodes of linked list.
// The boolean flag isOdd is used to find if the current
// node is even or odd.
void printAlternate(struct Node* node, bool isOdd=true)
{
    if (node == NULL)
       return;
    if (isOdd == true)
        cout << node->data << " ";
    printAlternate(node->next, !isOdd);
}
 
// Driver code
int main()
{
    // Start with the empty list
    struct Node* head = NULL;
 
    // construct below list
    // 1->2->3->4->5->6->7->8->9->10
 
    push(&head, 10);
    push(&head, 9);
    push(&head, 8);
    push(&head, 7);
    push(&head, 6);
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);
 
    printAlternate(head);
 
    return 0;
}

Java




// Java code to print alternate nodes
// of a linked list using recursion
class GFG
{
 
// A linked list node
static class Node
{
    int data;
    Node next;
};
 
// Inserting node at the beginning
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;
}
 
// Function to print alternate nodes of linked list.
// The boolean flag isOdd is used to find if the current
// node is even or odd.
static void printAlternate( Node node, boolean isOdd)
{
    if (node == null)
    return;
    if (isOdd == true)
        System.out.print( node.data + " ");
    printAlternate(node.next, !isOdd);
}
 
// Driver code
public static void main(String args[])
{
    // Start with the empty list
    Node head = null;
 
    // construct below list
    // 1.2.3.4.5.6.7.8.9.10
 
    head = push(head, 10);
    head = push(head, 9);
    head = push(head, 8);
    head = push(head, 7);
    head = push(head, 6);
    head = push(head, 5);
    head = push(head, 4);
    head = push(head, 3);
    head = push(head, 2);
    head = push(head, 1);
 
    printAlternate(head,true);
 
}
}
 
// This code is contributed by Arnab Kundu

Python3




# Python3 code to print alternate nodes
# of a linked list using recursion
 
# A linked list node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Inserting node at the beginning
def push( head_ref, new_data):
 
    new_node = Node(new_data);
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    return head_ref;
 
# Function to print alternate nodes of
# linked list. The boolean flag isOdd
# is used to find if the current node
# is even or odd.
def printAlternate( node, isOdd):
    if (node == None):
        return;
    if (isOdd == True):
        print( node.data, end = " ");
    if (isOdd == True):
        isOdd = False;
    else:
        isOdd = True;
    printAlternate(node.next, isOdd);
 
# Driver code
 
# Start with the empty list
head = None;
 
# construct below list
# 1->2->3->4->5->6->7->8->9->10
head = push(head, 10);
head = push(head, 9);
head = push(head, 8);
head = push(head, 7);
head = push(head, 6);
head = push(head, 5);
head = push(head, 4);
head = push(head, 3);
head = push(head, 2);
head = push(head, 1);
 
printAlternate(head, True);
 
# This code is contributed by 29AjayKumar

C#




// C# code to print alternate nodes
// of a linked list using recursion
using System;
 
class GFG
{
  
// A linked list node
public class Node
{
    public int data;
    public Node next;
};
  
// Inserting node at the beginning
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;
}
  
// Function to print alternate nodes of linked list.
// The boolean flag isOdd is used to find if the current
// node is even or odd.
static void printAlternate( Node node, bool isOdd)
{
    if (node == null)
    return;
    if (isOdd == true)
        Console.Write( node.data + " ");
    printAlternate(node.next, !isOdd);
}
  
// Driver code
public static void Main(String []args)
{
    // Start with the empty list
    Node head = null;
  
    // construct below list
    // 1.2.3.4.5.6.7.8.9.10
  
    head = push(head, 10);
    head = push(head, 9);
    head = push(head, 8);
    head = push(head, 7);
    head = push(head, 6);
    head = push(head, 5);
    head = push(head, 4);
    head = push(head, 3);
    head = push(head, 2);
    head = push(head, 1);
  
    printAlternate(head,true);
  
}
}
 
// This code has been contributed by 29AjayKumar

Javascript




<script>
// javascript code to print alternate nodes
// of a linked list using recursion     // A linked list node
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}
 
 
    // Inserting node at the beginning
    function push(head_ref , new_data) {
var new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }
 
    // Function to print alternate nodes of linked list.
    // The boolean flag isOdd is used to find if the current
    // node is even or odd.
    function printAlternate(node,  isOdd) {
        if (node == null)
            return;
        if (isOdd == true)
            document.write(node.data + " ");
        printAlternate(node.next, !isOdd);
    }
 
    // Driver code
     
        // Start with the empty list
var head = null;
 
        // construct below list
        // 1.2.3.4.5.6.7.8.9.10
 
        head = push(head, 10);
        head = push(head, 9);
        head = push(head, 8);
        head = push(head, 7);
        head = push(head, 6);
        head = push(head, 5);
        head = push(head, 4);
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 1);
 
        printAlternate(head, true);
 
// This code contributed by umadevi9616
</script>

Output: 

1 3 5 7 9

 


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