反转链表

输入一个链表，反转链表后，输出新链表的表头。

public ListNode ReverseList(ListNode head) {
        if(head != null){
            ListNode result = new ListNode(head.val);
            ListNode rt = result;
            Stack<ListNode> stack = new Stack<ListNode>();
            while(head != null){
                stack.push(new ListNode(head.val));
                head = head.next;
            }
            result.val = stack.pop().val;
            while(!stack.empty()){
                result.next = new ListNode(stack.pop().val);
                result = result.next;
            }
            return  rt;
        }
        return null;
    }