The Train Heist | Think Like A Coder, Ep 4

譯者: Clement Fu 審譯者: Helen Chang

[TED-Ed 原創系列]

《時代女神 x 程式邏輯革命》

[地點：八達圍]

[第四集：掠過]

Ethic, Hedge, and Adila, the leader of the revolution,

彥霖、凌杰和光復領袖艾德拉

plot out how they can steal an artifact called the Node of Power.

從長計議「力量之泉」的神偷妙計

It’s being used to run a heavily fortified train that runs all around the country,

這枚瑰寶推動穿梭全國的重裝列車

providing supplies to settlements and facilities.

補給各殖民地及基地設施

This armored behemoth

憚赫千里、龐大無比的裝甲列車

undergoes a complex and unpredictable unloading procedure—

到站後的卸載程序複雜難測

a procedure which is displayed, in detail, on a screen within the engine car.

卻在引擎室的螢幕上一清二楚

Right means the train will go one car length forward,

右箭頭表示列車前行一節車廂

and left means the train will go the same distance backwards.

左箭頭則是倒退一節車廂

While unloading, the train frequently moves back and forth,

卸載時，列車經常前後往復

so a typical sequence might look like this.

流程看起來就是這樣子

Also within the engine car is a button that can only be pressed once.

引擎室也有只許按下一次的按鈕

When pressed, it lets down the force field over the artifact for 10 seconds.

按下會解除環繞瑰寶的力場 10 秒

The engine car is tiny and designed for a robot.

引擎室為機器人設計，非常狹小

Of your team, only Hedge can fit.

三人行，只有凌杰鑽得進去

The members of the resistance have positioned a crane over the train tracks

光復手足已在鐵路旁架好吊車

that can pluck the artifact once it’s exposed.

時機一到，就可掠走瑰寶

They’ll know when to lower the crane by sight.

吊臂該何時降下，可靠目測

But the only way Hedge can determine the train’s position

另一方面，要判斷列車所在的位置

and know when to lower the force field

以及該何時解除瑰寶的力場光環

is by analyzing the unloading procedure,

凌杰還得分析卸載程序才知道

because he’ll be inside the windowless engine car.

因為他將身處四面無窗的引擎室

Hedge can’t program himself though, so it’s up to Ethic to tell him what to do.

凌杰不會自己寫程式，惟有靠彥霖

The artifact is in the car 10 positions behind

一開始列車到站時，瑰寶那節車廂

the one that’s directly under the crane at the start.

就在吊車下的車廂往後數第 10 節

What instructions can Ethic give Hedge

彥霖該如何指示凌杰

so that he hits the button at just the right moment?

於正確時機按下按鈕？

Here’s a hint to get you started.

先給大家一個秘訣

The key to this problem, as with many programming challenges,

解題關鍵諸如其他程式設計難題

is to reframe the information in a way that a computer can work with.

是把資訊重組成供電腦處理的框架

A computer doesn’t know what a train is, nor does it need to.

電腦不知道何謂列車，也毋需知道

It can, however, work with variables.

不過，電腦懂得處理變數

Try making a variable that tracks the train’s position.

試試拿一個變數來追蹤車廂位置

How will it change as the train moves?

列車挪動時，變數該如何變化？

Let’s start by breaking this problem into two objectives.

這道題一開始不如拆分成兩個目標

The first is to know where the train will be as it carries out its instructions.

一是得悉列車按指示挪動時的位置

The second is to hit the button when the train is in just the right position.

二是當目標車廂到位時就按下按鈕

For the first objective it’ll help to think of the train as a big number line.

首個目標可視列車為長長的數字線

Let’s make 0 the car with the node, 1 the car in front of it, and so on.

0 是瑰寶所在車廂，前面的是 1

That means car 10 is under the crane at the start.

如此類推，10 就是吊車下的車廂

When the train moves one car right, car 9 is under the crane.

列車右挪一下，吊車下就是車廂 9

So a right arrow can be thought of as “subtract 1.”

右箭頭可想像成「減 1」

And when the train moves left from there,

當列車左挪一下，吊車下又重回 10

10 is back under the crane,

making a left arrow the same as “add 1."

左箭頭等如「加 1」

Let’s set our train position variable to 10, since that’s where we start.

車廂位置變數設成 10 即開始位置

We can now use a loop to read the instructions one at a time,

之後就可用迴圈逐一讀取列車指示

adding or subtracting as we go, to track which car is under the crane.

每次加一或減一追蹤吊車下的車廂

The nice thing about setting up the variable this way

這樣設定變數

is that it tells us how far the node is from the crane.

好讓我們知道吊車與瑰寶的距離

So as soon as the variable hits 0, Hedge should hit the button.

一俟變數為 0，凌杰就應該按下按鈕

And here’s what happens.

言歸正傳

Ethic gets into position on the crane while Hedge rushes off

彥霖躍上吊臂待命

and slips into the engine car unnoticed, just before the train lurches to life.

列車起動時凌杰也剛好竄進引擎室

It rolls 3 cars back. 1 forward, another 4 back.

之後倒退 3 節、前進 1 節、後退 4 節

Then so far forward Ethic loses track before it reverses once more.

前進不知幾多節再後退，彥霖儍眼

When the artifact finally rolls into position,

當瑰寶到位時，艾德拉降下吊臂

Adila lowers the crane, hoping Ethic and Hedge got it right.

餘下的就交棒彥霖、凌杰

At the last possible moment, the force field sputters and falls.

千鈞一髮，力場光環熄滅

Ethic swoops in, and lifts the Node of Power to freedom.

彥霖擒拿力量之泉掠過自由的天空

When Ethic gives the node to Hedge for safe keeping,

正當彥霖把瑰寶交給凌杰保管

something incredible happens.

不可思議的事情發生了

The artifact shimmers to life with a vision of the past:

瑰寶熠熠生輝，掠過一幕幕過去

When the crystal was unearthed, no one could make the console inside work.

剛出土時水晶內的主控台與人絕緣

The government put out a call for people to try their luck with it,

政府旁求俊彥逐一碰運氣鑿開混沌

one at a time.

化頑石為靈石

Ethic loved to figure out what made things tick, so she signed up.

彥霖一向好奇事物原理，於是自薦

Within moments at the console, something clicked into place,

埋首主控台不久，彥霖妙手通竅

and she created her first robot.

創造了她第一個機器人

The government hired Ethic as chief robotics engineer on the spot.

政府即席羅致她為機器人總工程師

Within a year her creations ran almost every aspect of society,

不足一年女神的造物幾乎鋪天蓋地

成為社會的中流砥柱，民殷國富

and the nation and its people thrived,

no longer needing to toil in the fields and factories.

上至廠房下至田野都不用蒼生勞苦

The vision ends, and Hedge detects the second artifact in the 198forest,

顯現的往事到此為止，凌杰偵測到

第二枚瑰寶就在東南方一九八樹林

to the southeast.

Luckily, the train is going there next,

可幸，列車下一站正駛往那個地方

and has just enough reserve fuel for the trip.

列車的備用燃料也該熬得過去

Ethic and Hedge smuggle themselves aboard

彥霖、凌杰偷偷躥上列車藏身暗角

and find a hiding spot for the long journey ahead.

在夜沉沉、路遙遙的旅途邁向黎明