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) {
        Stack<ListNode> stack = new Stack<>();
        while (head != null) {
            stack.push(head);
            head = head.next;
        }
        if (stack.isEmpty()) {
            return null;
        }
        ListNode node = stack.pop();
        ListNode temp  = node;
        while (!stack.isEmpty()) {
            ListNode tempNode = stack.pop();
            node.next = tempNode;
            node = node.next;
        }
        // 将head头节点置为null
        node.next =null;
        return temp;
    }
}