刷题-链表翻转

import java.util.ArrayList;
public class Solution {
    public ArrayList printListFromTailToHead(ListNode listNode) {
        ArrayList outputList = new ArrayList<>();
        while(listNode != null) {
            outputList.add(listNode.val);
            listNode = listNode.next;
        }
        ArrayList outputArray = new ArrayList<>();
        for(int i=0;i 
 
递归——永远学不会用递归系列 
链表太长，会报错，Exception in thread “main” java.lang.StackOverflowError
 
import java.util.ArrayList;
public class Solution {
    ArrayList outputList = new ArrayList<>();
    public ArrayList printListFromTailToHead(ListNode listNode) {
        dfs(listNode);
        return outputList;
    }
    void dfs(ListNode listNode){
        if(listNode == null){
            return;
        }
        dfs(listNode.next);
        outputList.add(listNode.val);
    }
}
 
栈Stack 
利用栈先进后出的特点
 
import java.util.*;
public class Solution {
    ArrayList outputList = new ArrayList<>();
    Stack stack = new Stack<>();
    public ArrayList printListFromTailToHead(ListNode listNode) {
        while(listNode != null){
            stack.push(listNode.val);
            listNode = listNode.next;
        }
        while(!stack.empty()){
            outputList.add(stack.pop());
        }
        return outputList;
    }
}