反轉鏈表

題目描述：輸入一個鏈表，反轉鏈表。

參考代碼：

import java.util.ArrayList;
public class Solution {
    public ListNode ReverseList(ListNode head) {
        if(head == null){
            return null;
        }
        int len = 0;
        ArrayList<Integer> list = new ArrayList();
        ListNode node = head;
        while(node != null){
            list.add(node.val);
            node = node.next;
        }
        ListNode newHead = new ListNode(list.get(list.size() - 1));
        node = newHead;
        for(int i = list.size() -2; i >= 0; i--){
            ListNode no = new ListNode(list.get(i));
            node.next = no;
            node = node.next;
        }
        return newHead;

    }
}