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• After breaking Ethic out of prison,

• Hedge flies them both towards a frontier settlement

• in the shadow of the Bradbarrier, the great wall that encircles the nation.

• All the settlers there will soon gather for the monthly feeding.

• The people of the wall spend their days gathering up works of art and literature,

• from all across the land.

• On feeding day, the furnace-bots arrive, ravenous.

• If they eat, the lights stay on, and the food gets delivered.

• If they starve, the people do too.

• Hedge's fuel supply runs out just as he and Ethic reach the outskirts of town,

• and they come in for a crash landing.

• Luckily, everyone is too busy preparing for the feeding to notice.

• Today's feeding is where Ethic can find the leader

• of an underground resistance movement.

• This person knows the location of the first of three powerful artifacts.

• The problem is, Hedge and Ethic don't know

• the resistance leader's name or appearance.

• But Hedge has gathered the following information:

• The leader has green eyes.

• If the leader has red hair, their name has at least one consecutive double letter.

• If the leader wear glasses, their name has exactly 2 vowels.

• Otherwise, their name has exactly 3 vowels.

• There is exactly one person for whom these are all true.

• As a fugitive,

• Ethic can't sneak into the crowd without drawing attention to herself.

• But she can give instructions to Hedge.

• And one tool she has is what programmers call a conditional.

• That's a statement of the formIf A, then B.”

• Flowcharts are great illustrations of how those work.

• This conditional translates to: if A is true, carry out instruction B.

• There are also conditionals that account for different possibilities.

• This says, “If A is true, perform instruction B.

• Otherwise, carry out instruction C.”

• So what instructions does she give Hedge so he can find the resistance leader?

• Pause now to figure it out for yourself.

• With a problem like this, it can help to simplify first.

• What if Hedge just has to examine this one person?

• What information does he need to collect about her?

• He might ask, “Does she have green eyes?”

• What other questions should Hedge ask to find the resistance leader,

• and how can he track those answers?

• Pause now to figure it out for yourself.

• It may seem intuitive how you'd approach this problem as a human.

• But Hedge isn't a human,

• and so the challenge comes from needing to give him systematic instructions

• that will work in any scenario.

• Hedge needs to examine the settlers, one at a time,

• until he discovers the right person.

• In other words, like with the lock on the prison cell,

• this is a loop that repeats the same instructions.

• Only this time the loop will involve a series of questions

• in the form of conditionals,

• and will end as soon as Hedge finds his target.

• But first, you'll want to organize your information.

• Each person has a set of characteristics: Eye color, hair color, glasses, and name.

• Does this person have green eyes?

• If so, mark a check next toeye color." If not, mark an X there.

• If they have red hair, does their name contain a double letter?

• If so, mark a check next tohair color.”

• If they don't have a double letter, mark an X next tohair color.”

• Anyone with red hair and no double letter can't be the resistance leader.

• But notice that if they have blue hair,

• Hedge will skip this question and go on to the next one.

• For the last question, we can say,

• If they wear glasses, does their name have exactly 2 vowels?

• If they don't have glasses, does their name have exactly 3 vowels?”

• There will be people in the crowd with glasses and 1 vowel,

• or no glasses and 2 vowels.

• But they're not who we're looking for, so they'll get X's.

• The resistance leader must be someone with either check marks

• or blanks next to every question.

• Blanks are ok, because if someone has blue hair,

• the rule about red hair doesn't apply to them.

• You could have Hedge ask every question about every person,

• and then choose the person with only checks and blanks.

• But there's a way to save yourself lots of time: as soon as Hedge marks an X,

• have him move on to the next person.

• You don't need to know the answer to every question;

• just one X means they're not the target of your search.

• Hedge buzzes through the crowd,

• and within minutes finds Adila, the resistance leader,

• and brings her back to Ethic.

• Adila agrees to help them steal the first artifactthe node of power

• but under one condition:

• that Ethic and Hedge jump-start the revolution

• by reprogramming the furnace-bots that terrorize the town.

• And right on cue, the robots descend.

After breaking Ethic out of prison,

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# The Resistance | Think Like A Coder, Ep 2

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ktyvr258 posted on 2019/10/22
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