The Train Heist | Think Like A Coder, Ep 4

翻译人员: Carol Wang 校对人员: Jiasi Hao

[ 像程序员一样思考 ]

[ 地点：BRADBARRIER ]

[ 第四集 劫持火车 ]

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

艾斯克、海吉和革命领袖埃迪拉

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

制定了偷取神器“能量晶石”的方案。

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

它被用来运行重点防御的一列火车，

该专列负责为全国的定居点 和设施提供物资。

providing supplies to settlements and facilities.

This armored behemoth

这个庞然大物全副武装，

undergoes a complex and unpredictable unloading procedure—

其卸货过程 非常复杂且不可预测——

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

该过程详细显示在 发动机车厢内的屏幕上。

Right means the train will go one car length forward,

向右的箭头表示 火车向前行驶一节车厢的距离，

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

而向左的箭头则表示 火车向后行驶相同的距离。

While unloading, the train frequently moves back and forth,

卸货期间，火车会不停地来回开动，

so a typical sequence might look like this.

因此，一个典型的移动顺序 可能是这样的。

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

此外，在发动机车厢内还有一个按钮， 该按钮只能按下一次。

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

按下后，将有 10 秒 解除对能量晶石的控制。

The engine car is tiny and designed for a robot.

发动机车厢很小，专为机器人设计。

Of your team, only Hedge can fit.

在你们的团队中，只有海吉进得去。

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

抵抗组织成员已在车轨上方 安置了一台起重机，

that can pluck the artifact once it’s exposed.

能量晶石一旦显现， 即可以将其快速取出。

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

他们能目测何时降下起重机，

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

但是，因为海吉将置身于 无窗的发动机车厢内，

and know when to lower the force field

看不到车外情况，

is by analyzing the unloading procedure,

它只能通过分析卸货过程，

because he’ll be inside the windowless engine car.

才能确定火车的位置 并明确何时释放力场以解除晶石控制。

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

海吉自己不懂编程， 所以需要艾斯克告诉它怎么做。

The artifact is in the car 10 positions behind

从起重机所在车厢处算起，

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

能量晶石在第 10 节车厢。

What instructions can Ethic give Hedge

艾斯克可以给予海吉什么指示，

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

以便它在适当的时候按下按钮呢？

[ 5 秒后公布规则 ]

若想自己解题，可暂停播放。

[ 5 秒后公布规则 ]

Here’s a hint to get you started.

解题提示：

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

与许多编程挑战一样，

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

解题关键，就是用计算机 运行方式来重构信息。

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

计算机不知道火车是什么， 也不需要知道，

It can, however, work with variables.

但是，它可以使用变量。

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

可尝试定义一个跟踪火车位置的变量，

How will it change as the train moves?

看看随着火车的移动 它会如何变化呢？

[ 5 秒后公布答案 ]

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

就从将问题分为两个目标入手吧。

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

首先，要确定火车执行卸货指示时的位置，

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

其次，在火车处于正确位置时按下按钮。

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

对于第一个目标，把火车当做 一个大数轴理解就容易多了，

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

把能量晶石所在的车厢设为 0， 它前面的车厢设为 1，依此类推，

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

得出车厢 10 位于起重机下方。

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

当火车向右移动一节车厢时， 车厢 9 位于起重机下方。

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

因此，可将向右箭头视为“ - 1 ”。

And when the train moves left from there,

当火车再向左移动时， 车厢 10 将回到起重机下方，

10 is back under the crane,

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

即向左箭头等同于“ + 1 ”。

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

我们从起重机下方的车厢开始， 那应把火车位置变量设为 10 。

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

我们现在用循环语句读取指示， 一次读一条指示，

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

边读边对位置变量进行加减运算，

得出起重机下的车厢编号。

The nice thing about setting up the variable this way

这样设置变量的好处是，

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

它可以直接告诉我们 能量晶石距起重机有多远。

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

因此，只要变量等于 0， 海吉就应该按下按钮。

And here’s what happens.

下面就是实际操作。

Ethic gets into position on the crane while Hedge rushes off

在火车开始移动之前，

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

海吉冲出去并滑入发动机车厢，

艾斯克进入起重机就位。

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

火车先后退 3 节车厢， 又前进 1 节，再后退 4 节，

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

此时，艾斯克已茫然不知 起重机下是哪节车厢。

When the artifact finally rolls into position,

当能量晶石终于处于起重机正下方时，

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

埃迪拉放下起重机，

并希望艾斯克和海吉能操作无误，

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

在最后可能的时刻， 力场轰然崩塌。

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

艾斯克冲过去， 成功拿到了能量晶石。

When Ethic gives the node to Hedge for safe keeping,

当艾斯克把它交给海吉安全保管时，

something incredible happens.

不可思议的事情发生了。

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

能量晶石闪烁的光芒中 闪现出过去发生的一幕幕：

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

水晶刚出土的时候， 没人能使其内部控制台工作。

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

政府呼吁群众都来试试运气，

one at a time.

每个人试一次。

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

艾斯克想弄清水晶滴答作响的原委， 就报名了。

Within moments at the console, something clicked into place,

她登上控制台的片刻间， 一片声音响起，又回归安静。

and she created her first robot.

她就这样创造了自己的第一个机器人。

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

政府当场就聘请艾斯克 为首席机器人工程师。

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

在不到一年的时间里， 她创造的机器人几乎遍及各个角落，

and the nation and its people thrived,

国家及人民繁荣昌盛，

no longer needing to toil in the fields and factories.

不用再在工厂和田野里劳作。

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

历史影像播放结束， 海吉发现第二件神器在 198 森林，

to the southeast.

东南方。

Luckily, the train is going there next,

幸运的是，火车接下来就去那里，

and has just enough reserve fuel for the trip.

并且有足够燃料储备抵达。

Ethic and Hedge smuggle themselves aboard

艾斯克和海吉悄悄登车，

and find a hiding spot for the long journey ahead.

为接下来的漫长旅程 找到了藏身之所。