题解 | #反转链表#

 ListNode p=null,q=head;
        while(q!=null && q.next!=null){
            ListNode t = q.next;
            q.next = p;
            p = q;
            q = t;
        }
        if(q!=null) q.next = p;
        return q;
        

 if(head==null || head.next==null){ //如果后面没有或者自己就没有了 递归出去
            return head;
        }
        ListNode next = head.next; //next node
        ListNode reverse = ReverseList(next);//不管具体细节 假设后面翻转结束
        next.next = head;
        head.next = null;
        return reverse;

if(head==null) return null;
        Stack<ListNode> st = new Stack<ListNode>();
        while(head!=null){
            st.push(head);
            head = head.next;
        }
        ListNode ans = st.pop();
        ListNode t = ans;
        while(!st.isEmpty()){
            ListNode tt = st.pop();
            t.next = tt;
            t = tt;
        }
        t.next = null;
        return ans;