题解 | #反转链表#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @return ListNode类
     */
    public ListNode ReverseList (ListNode head) {
        // write code here
        if (head == null || head.next == null) {
            return head;
        }

        Stack<ListNode> stack = new Stack<>();
        while (head != null) {
            stack.add(head);
            head = head.next;
        }

        ListNode retHead = stack.pop();
        head = retHead;
        do {
            ListNode node = stack.pop();
            retHead.next = node;

            retHead = node;
        } while (!stack.isEmpty());
        retHead.next = null;
        return head;
    }
}