are a success!

壞消息是，你不小心

The bad news is that you accidentally

給了它們發射致命雷射的能力……

just gave them the ability to shoot deadly lasers

且你無法把它關掉。

…and you can't turn it off.

你有五分鐘可以阻止它們，

You have five minutes to stop them

然後雷射就會連線。

before the lasers go online.

在那之前，你所有的機器螞蟻

Until then,

都會在它們的棲息地裡行走，

all of your robo-ants will walk

速度剛好是每分鐘一公尺。

inside their habitat at a speed of

如果它們撞到或是碰到死路，

exactly 1 meter per minute.

它們會馬上回轉，從原路走回去。

If they bump into each other or hit a dead end,

五分鐘過後，它們就會啟動雷射，

they'll instantly turn around

脫身獲得自由，湧入世界中，

and walk back the way they came.

所經之處都會造成毀滅。

When five minutes are up,

你有一個機會阻止它們，

they'll turn on their lasers,

就是把兩個緊急用 真空吸塵器的管嘴插入棲息地中，

break free,

在螞蟻脫身之前把它們吸光。

and stream out into the world,

用力壓管嘴，就可以讓它 穿過棲息地前面的覆蓋薄膜，

carving a path of destruction as they go.

進入棲息地中的任何一處。

Your one chance to stop them is to insert

任何經過的螞蟻

the two emergency vacuum nozzles into the habitat

都會被吸起來並停止運作。

and suck the ants up before they break free.

管嘴放好之後就無法再移動，

The nozzles can press into any one location

一移動就會留下一個洞 讓機器螞蟻逃出來，

in the habitat through a membrane covering

所以關鍵是要選擇正確的插入點。

its front side, and any ants that walk past

棲息地是用一公尺長的 管子做成的。

will be sucked up and deactivated.

當機器螞蟻到了交叉口時，

You can't move the nozzles once they're placed

它們會隨機選擇要 左轉、右轉，或直走。

without leaving a hole that the robo-ants

會回轉的情況只有撞到

would pour out of, so choosing the

另一隻機器螞蟻或是碰到死路。

right spots will be key.

不幸的是，在棲息地中 有數百隻螞蟻，

The habitat is made out of meter-long tubes.

只要有一隻逃脫， 就會造成很大的傷害。

When the robots reach an intersection,

只剩下不到五分鐘，

they will pick randomly whether to go

你應該要把這兩個真空 吸塵器的管嘴放在哪裡

left, right, or forward.

才能把所有機器螞蟻都吸起來？

They only go backward if they hit

機器螞蟻在棲息地中到處跑，

hit another robo-ant or a dead end.

看起來似乎無法在它們 逃出去之前阻止它們。

Unfortunately, there are hundreds of them

但這個情況其實 比看起來的還容易解決。

inside the habitat, and if even one escapes,

原因如下。

it'll do a lot of damage.

想像只有兩隻機器螞蟻， 它們在爬向彼此。

With just less than five minutes remaining,

當它們相撞時，它們 馬上就會轉向反方向。

where should you place the 2 vacuum nozzles

如果它們改成是爬過彼此，

to suck up all the robo-ants?

那一連串事件 看起來會是什麼樣子？

Pause the video now if you want to figure it out for yourself.

在它們相撞之前和之後

Answer in: 3

看起來會完全一樣，

Answer in: 2

但它們位置會互換。

Answer in: 1

每當有一對螞蟻相碰時都是如此。

With robo-ants ricocheting all over the habitat,

因為每一隻螞蟻的 個別身分並不重要，

it might seem impossible to stop them

你只需要想出你要把管嘴放在哪裡

before they break free.

才能捕捉到每一隻螞蟻，

But this situation is simpler than it seems.

且每隻螞蟻都會從 棲息地的任何地方

Here's why.

開始不間斷地行走 不到五分鐘的時間。

Imagine just two robo-ants crawling

這樣就比較容易概念化和解題了。

toward each other.

把管嘴放在三或四根管子的交叉口

When they collide, they immediately

似乎是最有勝算的選擇，

reverse directions.

因為若不放在那裡， 機器螞蟻可能會改變方向，

And what would that sequence of events look

錯過你的管嘴。

like if they crawled past each other instead?

只有四個交叉口……

It would look exactly the same before

你會挑哪兩個？

and after their collision, but with

一定得選右上的交叉口。

their positions swapped.

如果沒有選它，當一隻螞蟻 從這個交叉口向下爬，

This is true every time a pair of robo-ants meet.

到達死路之後，

Because the identities of individual ants

就會花四分鐘爬回到這個交叉點，

don't matter, you just need to figure out where

接著往另外三個方向之一前進，

you should put the nozzles to capture

再走至少一分鐘。

any single ant walking without interruption

當你把一隻管嘴放在右上之後，

for less than 5 minutes, starting from

唯一有可能的選擇就是左下角了。

any point in the habitat.

若想知道它如何運作，

That's much easier to conceptualize and solve.

想像在棲息地中的任何 其他一處有一隻螞蟻。

Placing the nozzles at intersections where

最糟糕的狀況，這隻螞蟻 會從管嘴旁邊的點開始

three or four tubes meet seems like your best bet

朝遠離管嘴的方向爬。

since that's where the robo-ants might otherwise

但在所有最糟的情況下，

change directions and miss your nozzles.

螞蟻最多只能爬四公尺

There are only four intersections…

就會被吸到真空吸塵器中。

which two should you pick?

只有選這兩個交叉點，

The top right intersection has to be one of them.

才能保證在五分鐘內

If it isn't, an ant crawling down from

抓到所有的機器螞蟻。

this intersection toward the dead end would

把它們通通吸掉之後，

crawl for four minutes to get back to the

你阻止了一項重大危機。

intersection, and then go in any of three

在你下次要亂搞機器螞蟻之前，

directions, walking for at least another minute.

你會想要把機器食蟻獸先準備好。

Once you've placed a nozzle in the top right,

如果它還能飛行 和噴火，不是很酷嗎？

the only other choice that has a chance

那不可能會出錯的！

to work is the bottom left.

To see that this works, imagine an ant

anywhere else in the habitat.

Worst case scenario, the ant would start

right next to the vacuum nozzle, marching away from it.

But in all those worst cases, the ant would march

for at most 4 meters before being sucked

up into the vacuum.

No other choice of two intersection points

is guaranteed to get all the robo-ants

within five minutes.

Having vacuumed them all up, you've

averted a major crisis.

Before you mess with robo-ants again,

you'll want to have a robo-anteater ready.

And wouldn't it be cool if it could

fly and breathe fire?

There's no way that could go wrong!