从尾到头打印链表

剑指offer第五题，链表节点先入后出，想到用栈实现，代码如下

package com.zjy.sword2offer;

import java.util.Stack;

class ListNode{
	int val;
	ListNode next;
	
	ListNode(int value){
		val = value;
	}
}

public class PrintListReversely {

	public static void printListReversely(ListNode head){
		if(head==null)
			return;
		
		Stack<ListNode> sta = new Stack<ListNode>();
		ListNode current = head;
		
		while(current!=null)
		{
			sta.push(current);
			if(current.next!=null)
				current = current.next;
			else
				break;
		}
		
		while(!sta.isEmpty())
		{
			ListNode tmp = sta.peek();
			sta.pop();
			System.out.println(tmp.val);
		}
	}
}

当然用栈实现想到了递归，代码很简洁，但是效率较低

package com.zjy.sword2offer;

public class PrintListReversely_Recursively {
	
	public static void PrintRecursively(ListNode head){
		if(head==null)
			return;
		
		if(head.next!=null)
		{
			PrintRecursively(head.next);
		}
		
		System.out.println(head.val);
	}
}