【LeetCode 206】反转链表

    public static ListNode reverseList(ListNode head) {
    
    
    	if (head == null)
    		return null;
    	ListNode dummy = new ListNode();
    	dummy.next = head;
    	ListNode preNode = dummy;
    	ListNode p = head;
    	while (p != null)
    	{
    
    
    		ListNode rem = p.next;
    		p.next = preNode;
    		preNode = p;
    		p = rem;
    	}
    	head.next = null;
    	return preNode;
    }