Let us define a function on the circle: Start at any point, the value is the gasolin left in the car. (Negetive value allowed.) After each point, the value is increased by the amount of gasolin at that point. This function reaches its minimum at some point. That point is the starting point.
This function is 0 at its start point, (at 0+, it is the amount stored at the point - Our function is right continuous ) and it is back to 0 when it comes back to the same point. If we change the start point, the new function is the same shape but differs by a constant, so the new start point is 0. If we choose the minimum point to be our start point, the function is always non-negative. So we can have enough gas to come back.
哈哈哈哈 O(∩_∩)O哈哈~ 好久不来了，不小心看了一眼自己主页，发现自动关联了自己以往发过的帖，点进这个看了一眼，笑个半死。。。敢情我当初还发过这么搞笑的东西啊，我自己完全不记得了 
雷达卡
发表于 2005-3-22 17:59:00