题解 | #从尾到头打印链表#

import java.util.*;
/**
*    public class ListNode {
*        int val;
*        ListNode next = null;
*
*        ListNode(int val) {
*            this.val = val;
*        }
*    }
*
*/
import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ListNode curr = listNode;
        ArrayList<Integer> list =  new ArrayList<>();
        while (curr != null) {       
             list.add(curr.val);
              curr = curr.next;
        }
        //反转
        Collections.reverse(list);
        return list;
    }


    public ArrayList<Integer> printListFromTailToHead2(ListNode listNode) {
        //先反转
        ListNode curr = listNode;
        ListNode prev = null;
        while (curr != null) {
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;         
        }
        ArrayList<Integer> list =  new ArrayList<>();
        while (prev != null) {
            list.add(prev.val);
            prev = prev.next;
        }
        return list;
    }
}

我这里从尾到头打印链表有两个方案：

1、先遍历链表实现链表的反转，然后再次遍历装入 list 中

2、先遍历链表装入 list 中，然后通过 Collections.reverse 方法反转 list