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A hostile artificial intelligence called NIM has taken over the world's computers.
一个邪恶的人工智能，NIM，控制了全世界的电脑。
You're the only person skilled enough to shut it down, and you'll only have one chance.
你是唯一一个有能力关闭它的人，且你只有一次机会。
You've broken into NIM's secret lab, and now you're floating in a raft on top of 25 stories of electrified water.
你闯入了NIM的秘密实验室，现在正坐在浮在25层高的带电水上的一个皮筏艇里。
You've rigged up a remote that can lower the water level by ejecting it from grates in the sides of the room.
你已装配了一个遥控器，它可以通过把水从房间两侧的格子排走来降低水位。
If you can lower the water level to 0, you can hit the manual override, shut NIM off, and save the day.
如果你可以把水位降到0，你就可以按下手动操作按钮，关闭NIM并拯救世界。
However, the AI knows that you're here, and it can lower the water level, too, by sucking it through a trapdoor at the bottom of the lab.
但是这个AI知道你在这，它也能通过用实验室底部的活板门抽水，让水位降低。
If NIM is the one to lower the water level to 0, you'll be sucked out of the lab, resulting in a failed mission.
如果NIM把水位降低到了0，你就会被吸出实验室，从而导致任务失败。
Control over water drainage alternates between you and NIM, and neither can skip a turn.
你和NIM轮流排水，谁也不可以跳过任何一轮。
Each of you can lower the water level by exactly 1, 3, or 4 stories at a time.
你们俩每轮可以把水位降低刚好1层，3层或4层。
Whoever gets the level exactly to 0 on their turn will win this deadly duel.
谁在轮到自己时把水位降到了0谁就是这生死之战的赢家。
Note that neither of you can lower the water below 0; if the water level is at 2, then the only move is to lower the water level 1 story.
注意，你们俩谁都不能让水位降到0以下；假如水位在2，那你们就一次只能让水位降1层。
You know that NIM has already computed all possible outcomes of the contest, and will play in a way that maximizes its chance of success.
你知道NIM已经计算出了这场比赛的所有可能结果，而且它会选择以能让它自己赢的可能性最大化的方式来玩。
You go first. How can you survive and shut off the artificial intelligence?
你先出招。你要怎样才可以存活下来并终结这个人工智能呢？
You can't leave anything up to chance -- NIM will take any advantage it can get.
你不可以把任何一步交给命运--NIM会利用任何潜在优势。
And you'll need to have a response to any possible move it makes.
你得准备好应对NIM所有招数的措施。
The trick here is to start from where you want to end and work backwards.
这里的技巧是从理想结局开始进行倒推。
You want to be the one to lower the water level to 0, which means you need the water level to be at 1, 3, or 4 when control switches to you.
你想成为那个把水位降到0的人，意味着你需要水位在轮到你时在1，3或4的位置。
If the water level were at 2, your only option would be to lower it 1 story, which would lead to NIM making the winning move.
如果水位当时在2的位置，你唯一的选择便会是让水位降低1层，这就会让NIM获胜。
If we color code the water levels, we can see a simple principle at play:
如果我们用颜色标记一下这些水位，我们就会发现玩这个游戏的一个简单原则：
there are "losing" levels like 2, where no matter what whoever starts their turn there does, they'll lose.
游戏里存在一些“必输”层，比如第2层，一旦轮到那一层，无论是谁都必输无疑。
And there are winning levels, where whoever starts their turn there can either win or leave their opponent with a losing level.
游戏里也存在一些必胜层，无论是谁轮到那些层谁都能赢或是把他们的对手逼到必输层。
So not only are 1, 3, and 4 winning levels, but so are 5 and 6, since you can send your opponent to 2 from there.
所以不只是1，3和4是必胜层，5和6也是，因为从那些位置你可以把你的对手送到第2层。
What about 7? From 7, all possible moves would send your opponent to a winning level, making this another losing level.
那么第7层是什么情况呢？到了第7层，所有可能的移动都会把你的对手送到必胜层，所以这又是一个必输层。
And we can continue up the lab in this way.
我们可以继续这样往上推理。
If you start your turn 1, 3, or 4 levels above a losing level, then you're at a winning level. Otherwise, you're destined to lose.
如果轮到你时你在一个必输层上面1，3或4层的位置，那你就位于一个必胜层。否则，你必输无疑。
You could continue like this all the way to level 25.
你可以像这样一路推理到第25层。
But as a shortcut, you might notice that levels 8 through 11 are colored identically to 1 through 4.
不过还有一条捷径，你可能注意到了，第8到11层和第1到4层的颜色是一样的。
Since a level's color is determined by the levels 1, 3, and 4 stories below it,
由于层级的颜色取决于位于它下面1，3或4层的颜色，
this means that level 12 will be the same color as level 5, 13 will match 6, 14 will match 7, and so on.
所以第12层的颜色会和第5层的颜色一样，13会和6一样，14会和7一样，以此类推。
In particular, the losing levels will always be multiple of 7, and two greater than multiples of 7.
必输层的层数永远会是7的倍数，以及比7的倍数大2的数。
Now, from your original starting level of 25, you have to make sure your opponent starts on a losing level every single turn
现在，从你的出发点25层起，你得确保你的对手在任何一局中都位于必输层，
if NIM starts on a winning level even once, it's game over for you.
因为一旦NIM处于必胜层，哪怕是一次，你就完了。
So your only choice on turn 1 is to lower the water level by 4 stories.
所以在第一轮时你唯一的选择就是让水位降低4层。
No matter what the AI does, you can continue giving it losing levels until you reach 0 and trigger the manual override.
这样无论AI怎么做，你都可以把必输层推给它直到你到达第0层，启动手动操作装置。
And with that, the crisis is averted. Now, back to a less stressful kind of surfing.
这样危机就解除了。现在，回到一种更轻松的冲浪里吧。
