剑指offer03-从尾到头打印链表

从尾到头打印链表

题目描述

思路1

• 栈

/**
*code1
*/
import java.util.ArrayList;
import java.util.Stack;
    public static ArrayList<Integer> printListReverse1(ListNode headNode) {
        ArrayList<Integer> list = new ArrayList<>();
        Stack<ListNode> stack = new Stack<>();
        while (headNode != null) {
            stack.push(headNode);
            headNode = headNode.next;
        }

        while (!stack.isEmpty()) {
            list.add(stack.pop().val);
        }
        return list;
    }
    /**
*    public class ListNode {
*        int val;
*        ListNode next = null;
*
*        ListNode(int val) {
*            this.val = val;
*        }
*    }
*
*/

/**
*code2
*/
import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> list = new ArrayList<>();
        ListNode tmp = listNode;
        while(tmp!=null){
            list.add(0,tmp.val);
            tmp = tmp.next;
        }
        return list;
    }
}

思路2

• 递归

/**
*code1
*/
import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        if (listNode != null) {
            if (listNode.next != null) {
                list = printListFromTailToHead(listNode.next);
            }
            list.add(listNode.val);
        }
        return list;
    }
}