I remember long ago someone shared this problem with me and I wasn't able to finish it all. And since people around here seem to be pretty good with these so here it is.

Note I still don't know the answers.

2 People crash land on a planet (person A and B) and end up on 2 random points on the planet (sphere)

Under the following assumptions, what is the quickest way in which person A should find person B

1) person B stands still
2) person B wants to find person A as well
3) person B does not want person A to find him.

coolcrimefighter

United States378 Posts

April 21 2009 01:49 GMT

Its not something gay like "They both can't survive in space so they're both dead" is it?

ShinyGerbil

Canada519 Posts

April 21 2009 01:53 GMT

under no means is this for sure right, but it seems to me like 1) and 2) are the same, standing still is the most likely way to be found. and under each case, person A should just walk wherever he wants, without retracing his steps.

in 3), person B will just walk randomly, and so will person A...

Fontong

United States6454 Posts

April 21 2009 01:55 GMT

1) Probably person A should call person B and ask them where the fuck they are then go find their lazy ass

2) I guess person A can call person B and they could meet up at a coffee shop or something

3) I guess A has to look for B

Zozma

United States1626 Posts

April 21 2009 02:04 GMT

Meet at the wreckage of the spaceship, obviously.

Deleted User 3420

24492 Posts

April 21 2009 02:04 GMT

This question is weird. I don't understand how we can answer this without knowing more about the alien planet and the people who have crashed.

Do they have any equipment? What is the terrain like? Is there light? Is there water? Have person A and B discussed a strategy for this situation beforehand?

Are the 3 assumptions all combined into one question? Or are they 3 different scenarios ?

jeppew

Sweden471 Posts

April 21 2009 02:08 GMT

1. if B just sits still A will eventually find if he doesn't repeat his steps.

in 2 and 3 they can miss eachother and wander around forever.

Byo

Canada212 Posts

April 21 2009 02:09 GMT

they are variables.......... ie. under 1) the answer is for A to move in a spiral motion so it takes the least amount of time to cover the surface of the sphere.

I'm guessing 2) means that B will be moving in the same way as A... (they want to find each other)... but what that way is, i don't know.

Fontong

United States6454 Posts

April 21 2009 02:09 GMT

Imo this blog's title should be changed to "Deserted XCII"

And we seriously need an illustration -__-

Deleted User 3420

24492 Posts

April 21 2009 02:13 GMT

#10

On April 21 2009 11:09 Byo wrote:
they are variables.......... ie. under 1) the answer is for A to move in a spiral motion so it takes the least amount of time to cover the surface of the sphere.

ah so these problems are to be looked at mathematically then ?

It would seem to me that 1, 2, and 3 all have the same answer.

Divinek

Canada4045 Posts

April 21 2009 02:13 GMT

#11

Under the following assumptions, what is the quickest way in which person A should find person B

3) person B does not want person A to find him.

so shouldnt it be impossible if B is trying to hide from A?

I mean yeah I guess he's standing still, but what is point of the third option then if he cant hide?

Byo

Canada212 Posts

April 21 2009 02:15 GMT

#12

On April 21 2009 11:13 Divinek wrote:

Show nested quote +

so shouldnt it be impossible if B is trying to hide from A?

I mean yeah I guess he's standing still, but what is point of the third option then if he cant hide?

I believe its assumed that they have the same range of vision so if B sees A then A is able to see B

Byo

Canada212 Posts

April 21 2009 02:17 GMT

#13

On April 21 2009 11:13 travis wrote:

Show nested quote +

ah so these problems are to be looked at mathematically then ?

It would seem to me that 1, 2, and 3 all have the same answer.

yup all mathematically... I'm sure they don't have the same answer......

Mastermind

Canada7096 Posts

April 21 2009 02:20 GMT

#14

what makes this a nerdy question?

sixghost

United States2096 Posts

April 21 2009 02:20 GMT

#15

On April 21 2009 11:13 Divinek wrote:

Show nested quote +

so shouldnt it be impossible if B is trying to hide from A?

I mean yeah I guess he's standing still, but what is point of the third option then if he cant hide?

I think the difference in the 3rd problem is that you are supposed to assume that person B will move in a pattern that is not optimal for the two people to meet.

meeple

Canada10211 Posts

April 21 2009 02:26 GMT

#16

1) A quick exhaustive search of the sphere is the fastest method, If you imagine the sphere to be composed of a grid, there are a finite number of points to search and no best way to do it. Essentially its like asking whats the quickest way of looking in five holes... just look dammit.

2) The fastest way to find a person is if they stand still. So see the above answer. The reason for this is because this method is guaranteed to end, there are a finite number of places on the sphere and if they stay in one, they will eventually be found, which is why this is the method that search ad rescue crews tell people.

3) Well, you only have two options, you can either stay still or move around pretty randomly, and since staying still means you will eventually be found, then keep moving, and if you're really lucky, you can always avoid the person, but generally speaking you will avoid them for much longer than staying in the same spot.

Deleted User 3420

24492 Posts

April 21 2009 02:28 GMT

#17

On April 21 2009 11:20 sixghost wrote:

Show nested quote +

I think the difference in the 3rd problem is that you are supposed to assume that person B will move in a pattern that is not optimal for the two people to meet.

but no such pattern exists when he doesn't know what pattern the other guy will take

all moving does for person B is increase the variance in time it will take for person A to find him. It may make it faster, or it may make it slower. The average amount of time stays the same, no?

Carnivorous Sheep

Baa?21247 Posts

April 21 2009 02:30 GMT

#18

This isn't math.

Deleted User 3420

24492 Posts

April 21 2009 02:31 GMT

#19

I could understand this problem if:

1.) person B knew where person A landed
2.) person B knew that person A would take a pattern that maximized his odds of finding person B

Athos

United States2484 Posts

April 21 2009 02:37 GMT

#20

2) makes the most sense

If they both want to find each other than they will find each other. Hell, they may know something not mentioned.

And yeah, this is not math.

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