指定替换图片中颜色

快慢指针，注意下循环的终止条件

	public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummyHead = new ListNode();
        dummyHead.next = head;
        ListNode cur = dummyHead;
        ListNode slow = dummyHead;
        ListNode fast = dummyHead;
        while(n-- > 0){
            fast = fast.next;
        }
        while(fast.next != null){
            fast = fast.next;
            slow = slow.next;
        }
        slow.next = slow.next.next;
        return dummyHead.next;   
    }