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  • Ethic and her robot Hedge agree to help the resistance leader, Adila,

  • sabotage the art-incinerating furnace-bots.

  • In exchange,

  • Adila promises to lead them to the first object of Ethic's quest,

  • an artifact called the Node of Power.

  • Years ago, there was just one furnace-bot.

  • It had a 0 inside its furnace and an unknown,

  • randomly generated serial number.

  • Over time, the original self-replicated to produce more identical furnace-bots.

  • Each child inherited the original's unknown serial number within its furnace,

  • and had a random, unique serial number of its own inscribed on its shell.

  • The second generation of furnace- bots also self-replicated in the same way,

  • always passing their own serial numbers to their offspring's furnaces.

  • This continued on for many generations.

  • Today, each furnace-bot receives its orders from its parent.

  • So if Ethic can find the original 0 bot and somehow change its instructions,

  • she could take over the entire army, all at once.

  • Adila has the perfect solution:

  • a data crystal that she's been carrying for years,

  • waiting for the right moment to activate it.

  • It contains a program designed to gain control of a bot

  • and give it new instructions.

  • But if it's uploaded to any furnace- bot other than the original,

  • the 0 bot will override the instructions

  • and destroy the data crystal in the process.

  • The feeding is just a few minutes away,

  • and there's only one chance to get this right.

  • Fortunately, Hedge's ability to store data can help.

  • In programming,

  • a piece of information gets stored in something called a variable.

  • Variables are basically containers that hold onto numbers, words, or other values.

  • How does Ethic program Hedge to find the original 0 bot as quickly as possible?

  • Pause now to figure it out for yourself.

  • Here's a hint.

  • Programs can be written to have as many variables as you need,

  • but you can solve this problem with just one.

  • Hedge can use it to store a serial number

  • and replace it with a new one as often as he needs.

  • Pause now to figure it out for yourself.

  • A key insight here is that Hedge doesn't need to map out the entire

  • set of relationships to find the original furnace-bot.

  • If, for example, he gets lucky and picks the original one right away,

  • he'll be done.

  • But if he starts with any other bot,

  • he can still find a path that leads straight back to the 0-bot

  • by following a simple set of instructions.

  • To help craft them, let's first simplify the problem.

  • Let's say there were only three furnace-bots;

  • a parent and two children, but you don't know which is which.

  • You could have Hedge pick one at random and look inside its furnace.

  • Now, you know the family tree looks like this.

  • If the number inside the furnace is a 0, you've found the parent.

  • If not, then no matter which child you chose,

  • it must have the parent's serial number in its furnace.

  • So in this scenario, you're guaranteed to find the parent in one or two moves.

  • In actuality, there are many furnace-bots,

  • and you don't know how many generations there are

  • nor what the family tree looks like.

  • But you don't need to,

  • because Hedge can just keep repeating the same sequence of actions

  • until he gets to the original.

  • How? With a loop.

  • Hedge can pick any bot at random, look inside its furnace,

  • and store that serial number as a variable.

  • Then he'll begin the following loop that will repeat

  • until the stored variable equals 0,

  • the furnace number of the original bot:

  • 1. Find the bot whose shell serial number matches the stored number.

  • 2. Look inside its furnace.

  • 3. Store that new number, overwriting the old one.

  • Once the loop ends, we'll know that Hedge has found the 0 bot,

  • so he should upload the control program.

  • So here's what happens:

  • Hedge only takes 5 repetitions to find the original:

  • robot 733 has the 0 in its furnace.

  • In a blink of a mechanical eye,

  • the program spreads through the entire army, and Adila takes control.

  • She has the furnace-bots give off theatrical bouts of flame

  • to hide the fact that they're now secretly safe-guarding

  • all of that artistic output.

  • Now that Ethic's delivered the furnace-bots,

  • Adila honors her end of the deal.

  • She leads Ethic and Hedge to the location of the first artifact,

  • the Node of Power.

  • There, one thing is immediately clear:

  • they'll have to steal it.

Ethic and her robot Hedge agree to help the resistance leader, Adila,

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B1 US TED-Ed furnace hedge serial number serial ethic

The Furnace Bots | Think Like A Coder, Ep 3

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    ally.chang posted on 2020/02/26
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