给定一个链表，打印该链表的备用节点。 例如：
null
Input : 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9 -> 10Output : 1 -> 3 -> 5 -> 7 -> 9 Input : 10 -> 9Output : 10
递归方法： 1.初始化静态变量（比如标志） 2.如果标志为奇数，则打印节点 3.将head和flag增加1，并为下一个节点递归。
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> |
输出：
1 3 5 7 9
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