06-从尾到头打印链表

leetcode 链接：https://leetcode-cn.com/problems/cong-wei-dao-tou-da-yin-lian-biao-lcof/

题目

解法

1. 从头到尾遍历一次链表，值用栈保存，遍历到链表尾部后对栈中数据输出到数组中

   /**
   * Definition for singly-linked list.
   * public class ListNode {
   *     int val;
   *     ListNode next;
   *     ListNode(int x) { val = x; }
   * }
   */
   class Solution {
    public int[] reversePrint(ListNode head) {
        Stack<Integer> stack=new Stack<>();
        ListNode node=head;
        while(node!=null){
            stack.push(node.val);
            node=node.next;
        }
        int[] res=new int[stack.size()];
        int i=0;
        while(!stack.isEmpty()){
            res[i++]=stack.pop();
        }
        return res;
    }
   }

2. 对链表进行两次遍历，一次获取长度，一次填充数组

   /**
   * Definition for singly-linked list.
   * public class ListNode {
   *     int val;
   *     ListNode next;
   *     ListNode(int x) { val = x; }
   * }
   */
   class Solution {
    public int[] reversePrint(ListNode head) {
        // 使用两次遍历，一次获取链表长度，一次填充数组
        // 遍历游标
        ListNode cur = head;
        // 链表长度
        int len = 0;
        while (cur != null){
            len++;
            cur = cur.next;
        }
        int[] res = new int[len];
        // 重置遍历游标
        cur = head;
        while (--len >= 0){
            res[len] = cur.val;
            cur = cur.next;
        }
        return res;
    }
   }