题解 | #反转链表#

1. 使用栈是非常好的一个方法
2. import java.util.*;包含了很多工具

import java.util.*;
/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode ReverseList(ListNode head) {
        Stack<ListNode> stack = new Stack<>();
        //把链表结点都放到栈里
        while (head != null){
            stack.push(head);
            head = head.next;
        }
        if(stack.isEmpty())
            return null;
        ListNode node = stack.pop();
        ListNode dummy = node;
        while(!stack.isEmpty()){
            ListNode tempNode = stack.pop();
            node.next = tempNode;
            node = node.next;
        }
        node.next = null;
        return dummy;
    }
}