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

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

• providing supplies to settlements and facilities.

• This armored behemoth

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

• Right means the train will go one car length forward,

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

• so a typical sequence might look like this.

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

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

• The engine car is tiny and designed for a robot.

• Of your team, only Hedge can fit.

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

• that can pluck the artifact once it's exposed.

• They'll know when to lower the crane by sight.

• But the only way Hedge can determine the train's position

• and know when to lower the force field

• because he'll be inside the windowless engine car.

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

• The artifact is in the car 10 positions behind

• the one that's directly under the crane at the start.

• What instructions can Ethic give Hedge

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

• Here's a hint to get you started.

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

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

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

• It can, however, work with variables.

• Try making a variable that tracks the train's position.

• How will it change as the train moves?

• Let's start by breaking this problem into two objectives.

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

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

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

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

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

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

• So a right arrow can be thought of assubtract 1.”

• And when the train moves left from there,

• 10 is back under the crane,

• making a left arrow the same asadd 1."

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

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

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

• The nice thing about setting up the variable this way

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

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

• And here's what happens.

• Ethic gets into position on the crane while Hedge rushes off

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

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

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

• When the artifact finally rolls into position,

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

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

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

• When Ethic gives the node to Hedge for safe keeping,

• something incredible happens.

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

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

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

• one at a time.

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

• Within moments at the console, something clicked into place,

• and she created her first robot.

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

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

• and the nation and its people thrived,

• no longer needing to toil in the fields and factories.

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

• to the southeast.

• Luckily, the train is going there next,

• and has just enough reserve fuel for the trip.

• Ethic and Hedge smuggle themselves aboard

• and find a hiding spot for the long journey ahead.