You're the only person skilled enough to shut it down,

你是世界上唯一有足夠技能 可以將它關閉的人，

and you'll only have one chance.

你只有一次機會。

You've broken into NIM's secret lab,

你闖入了 NIM 的秘密實驗室，

and now you're floating in a raft on top of 25 stories of electrified water.

現在你坐在橡皮艇上， 漂浮在 25 層通電的水上。

You've rigged up a remote that can lower the water level

你草草做出了一個遙控器， 可以降低水位，

by ejecting it from grates in the sides of the room.

讓水從房間側邊的格柵排出。

If you can lower the water level to 0,

如果你能把水位降到 0，

you can hit the manual override,

你就可以進行手動覆寫，

shut NIM off,

將 NIM 關機，

and save the day.

拯救世界。

However, the AI knows that you're here, and it can lower the water level, too,

然而，人工智慧知道你在這裡， 且它也能夠降低水位，

by sucking it through a trapdoor at the bottom of the lab.

它的做法是從實驗室 底部的活板門將水吸出。

If NIM is the one to lower the water level to 0,

如果 NIM 將水位降到 0，

you'll be sucked out of the lab,

你就會被吸到實驗室外，

resulting in a failed mission.

任務就會失敗。

Control over water drainage alternates between you and NIM,

排水的控制權是由 你和 NIM 輪流取得，

and neither can skip a turn.

且誰都不可以跳過一輪。

Each of you can lower the water level by exactly 1,

你們兩個都能將水位 一次降低一層、

3,

三層或是四層。

or 4 stories at a time.

誰能在自己的那一輪 將水位剛好降至 0，

Whoever gets the level exactly to 0 on their turn

就能贏得這場生死對決。

will win this deadly duel.

要注意的是，你們兩個 都不能把水位降到比 0 更低；

Note that neither of you can lower the water below 0;

如果水位是在 2，

if the water level is at 2,

那麼唯一能做的就是 將水位降低一層。

then the only move is to lower the water level 1 story.

你知道 NIM 已經計算出了 這場比賽的所有可能結果，

You know that NIM has already computed all possible outcomes of the contest,

且一定會採取讓它的 成功機會最大的做法。

and will play in a way that maximizes its chance of success.

由你先控制。

You go first.

你要如何存活下來 並將人工智慧關閉？

How can you survive and shut off the artificial intelligence?

如果你想要自己解解看， 在這裡按暫停。

Pause here if you want to figure it out for yourself.

公佈答案倒數：三。

Answer in: 3

公佈答案倒數：二。

Answer in: 2

公佈答案倒數：一。

Answer in: 1

你不能完全靠運氣—— NIM 只要能佔便宜就一定會佔。

You can't leave anything up to chance - NIM will take any advantage it can get.

你得要針對它可能的 每一步棋做出反應。

And you'll need to have a response to any possible move it makes.

這裡的密訣在於要從 你想要的結果反向推導回來。

The trick here is to start from where you want to end and work backwards.

你想要成為將水位降至 0 的人，

You want to be the one to lower the water level to 0,

那就表示當你拿到 控制權時，水位必須是

which means you need the water level to be at 1, 3, or 4

在 1、3，或 4。

when control switches to you.

如果水位在 2，

If the water level were at 2,

你唯一的選擇就是降低一層，

your only option would be to lower it 1 story,

那就會讓 NIM 能做出 贏得勝利的一步。

which would lead to NIM making the winning move.

如果我們把水位用顏色編碼，

If we color code the water levels,

我們就能看出這裡 有個簡單的原則：

we can see a simple principle at play:

有「必輸」的樓層，比如 2，

there are “losing” levels like 2,

無論如何，到了那一層的人必輸。

where no matter what whoever starts their turn there does, they'll lose.

也有「必勝」的樓層， 如果你從那裡開始你的那一輪，

And there are winning levels, where whoever starts their turn there

你就會贏，或是讓你的對手 只能到達必輸的樓層。

can either win or leave their opponent with a losing level.

所以「必勝」樓層 不只是 1、3，和 4，

So not only are 1, 3, and 4 winning levels,

還有 5 和 6，

but so are 5 and 6,

因為從這兩層你都可以 把你的對手送到 2 。

since you can send your opponent to 2 from there.

那 7 呢？

What about 7?

從 7，不論你做什麼， 都會把你的對手送到必勝樓層，

From 7, all possible moves would send your opponent to a winning level,

因此 7 也是必輸樓層。

making this another losing level.

我們可以用這種方式 一路向上做判斷。

And we can continue up the lab in this way.

如果你是在必輸樓層 向上加一、三，或四層樓，

If you start your turn 1, 3, or 4 levels above a losing level,

那你就是在必勝樓層。

then you're at a winning level.

要不然，你就注定會輸。

Otherwise, you're destined to lose.

你可以一直這樣做，直到 25。

You could continue like this all the way to level 25.

但有個截徑，

But as a shortcut,

你可能會發現，樓層 8 到 11 和 1 到 4 有一樣的顏色。

you might notice that levels 8 through 11 are colored identically to 1 through 4.

因為一層樓的顏色是由它向下 一、三，及四層樓所決定的，

Since a level's color is determined by the levels 1, 3, and 4 stories below it,

這就表示樓層 12 和 5 的顏色會一樣，

this means that level 12 will be the same color as level 5,

13 和 6 會一樣，

13 will match 6,

14 和 7 會一樣，以此類推。

14 will match 7, and so on,

特別的是，必輸樓層 都一定是 7 的倍數，

In particular, the losing levels will always be multiple of 7,

以及 7 的倍數再加 2。

and two greater than multiples of 7.

現在，回到你最初的樓層 25，

Now, from your original starting level of 25,

你得要確保你的對手每一輪 都要從必輸樓層開始——

you have to make sure your opponent starts on a losing level every single turn—

如果 NIM 從必勝樓層開始，

if NIM starts on a winning level even once,

你就玩完了。

it's game over for you.

所以你第一輪唯一的選擇 就是向下降四層。

So your only choice on turn 1 is to lower the water level by 4 stories.

不論人工智慧做什麼，

No matter what the AI does,

你都可以持續一直給它必輸樓層，

you can continue giving it losing levels

直到你達到 0，進行人工覆寫。

until you reach 0 and trigger the manual override.

這麼一來，危機就解除了。

And with that, the crisis is averted.

現在可以回到比較 沒有壓力的上網瀏覽了。

Now, back to a less stressful kind of surfing.