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  • The good news is that your experimental robo-ants

  • are a success!

  • The bad news is that you accidentally

  • just gave them the ability to shoot deadly lasers

  • and you can't turn it off.

  • You have five minutes to stop them

  • before the lasers go online.

  • Until then,

  • all of your robo-ants will walk

  • inside their habitat at a speed of

  • exactly 1 meter per minute.

  • If they bump into each other or hit a dead end,

  • they'll instantly turn around

  • and walk back the way they came.

  • When five minutes are up,

  • they'll turn on their lasers,

  • break free,

  • and stream out into the world,

  • carving a path of destruction as they go.

  • Your one chance to stop them is to insert

  • the two emergency vacuum nozzles into the habitat

  • and suck the ants up before they break free.

  • The nozzles can press into any one location

  • in the habitat through a membrane covering

  • its front side, and any ants that walk past

  • will be sucked up and deactivated.

  • You can't move the nozzles once they're placed

  • without leaving a hole that the robo-ants

  • would pour out of, so choosing the

  • right spots will be key.

  • The habitat is made out of meter-long tubes.

  • When the robots reach an intersection,

  • they will pick randomly whether to go

  • left, right, or forward.

  • They only go backward if they hit

  • hit another robo-ant or a dead end.

  • Unfortunately, there are hundreds of them

  • inside the habitat, and if even one escapes,

  • it'll do a lot of damage.

  • With just less than five minutes remaining,

  • where should you place the 2 vacuum nozzles

  • to suck up all the robo-ants?

  • Pause the video now if you want to figure it out for yourself.

  • Answer in: 3

  • Answer in: 2

  • Answer in: 1

  • With robo-ants ricocheting all over the habitat,

  • it might seem impossible to stop them

  • before they break free.

  • But this situation is simpler than it seems.

  • Here's why.

  • Imagine just two robo-ants crawling

  • toward each other.

  • When they collide, they immediately

  • reverse directions.

  • And what would that sequence of events look

  • like if they crawled past each other instead?

  • It would look exactly the same before

  • and after their collision, but with

  • their positions swapped.

  • This is true every time a pair of robo-ants meet.

  • Because the identities of individual ants

  • don't matter, you just need to figure out where

  • you should put the nozzles to capture

  • any single ant walking without interruption

  • for less than 5 minutes, starting from

  • any point in the habitat.

  • That's much easier to conceptualize and solve.

  • Placing the nozzles at intersections where

  • three or four tubes meet seems like your best bet

  • since that's where the robo-ants might otherwise

  • change directions and miss your nozzles.

  • There are only four intersections

  • which two should you pick?

  • The top right intersection has to be one of them.

  • If it isn't, an ant crawling down from

  • this intersection toward the dead end would

  • crawl for four minutes to get back to the

  • intersection, and then go in any of three

  • directions, walking for at least another minute.

  • Once you've placed a nozzle in the top right,

  • the only other choice that has a chance

  • to work is the bottom left.

  • To see that this works, imagine an ant

  • anywhere else in the habitat.

  • Worst case scenario, the ant would start

  • right next to the vacuum nozzle, marching away from it.

  • But in all those worst cases, the ant would march

  • for at most 4 meters before being sucked

  • up into the vacuum.

  • No other choice of two intersection points

  • is guaranteed to get all the robo-ants

  • within five minutes.

  • Having vacuumed them all up, you've

  • averted a major crisis.

  • Before you mess with robo-ants again,

  • you'll want to have a robo-anteater ready.

  • And wouldn't it be cool if it could

  • fly and breathe fire?

  • There's no way that could go wrong!

The good news is that your experimental robo-ants

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B1 US TED-Ed robo habitat ant intersection vacuum

Can you solve the killer robo-ants riddle? - Dan Finkel

  • 55 5
    ally.chang posted on 2020/02/11
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