摘要：
看懂题目花了很长时间： 题目是这样的： 英文：There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third r 阅读全文
摘要：
Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respecti 阅读全文