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){
            return null;
        }
        ListNode p=head;
        Stack<Integer> stack=new Stack<>();
        while(p!=null){
            stack.add(p.val);
            p=p.next;
        }
        ListNode h=new ListNode(stack.pop());
        p=h;
        while(!stack.isEmpty()){
            ListNode tmp=new ListNode(stack.pop());
            p.next=tmp;
            p=tmp;
        }
        return h;
    }
}