Survival Puzzle

H

HLBennett

Joined
Jan 4, 2000
Messages
78
Here's a puzzle that is a variation on one that I have seen around the net as well as other places.

The particulars are this:

You and a friend have been sent to rescue two injured friends. An opposing force is looking for them as well. If they catch any member of your party it will go very badly for them. You have located the injured parties and only need to get them across a bridge to safety.(Charges are in place and you will blow it as soon as you cross.) The problem is that it is night and you have only one working flashlight. The bridge will only hold 2 people at a time. The opposing force is 17 minutes behind you. Everyone takes a different amount of time to cross the bridge.

You take 1 minute.
Your friend takes 2 minutes.
Injured Party #1 takes 5 minutes.
Injured Party #2 takes 10 minutes.
These are absolutes and cannot be changesd.

How do you get everyone across safely before the opposing force catches you? It can be done.
biggrin.gif


 
I forgot to mention that the flashlight is needed to cross. It must go back and forth until everyone is across...
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Doesn't seem too awfully difficult..., put Injured Party #2 out of his misery, and you'll have plenty of time
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Putting a man out of his misery is unacceptable. 10 minute man is the critical person. Tie a rope to one end of the bridge. Take 1&10 across. Tie a rope at the other end of the bridge. Send the flashlight to 2&5 using the rope. 2&5 untie rope and cross.
 
Putting a man out of his misery is unacceptable. 10 minute man is the critical person. Tie a rope to one end of the bridge. Take 1&10 across. Tie a rope at the other end of the bridge. Send the flashlight to 2&5 using the rope. 2&5 untie rope and cross.
 
The trick is to have the two slowest cross at the same time, so you and your friend cross, (2 min) then you go back with the light, (3 min), then send both injured across(13 min) give the light to your friend, who then goes back (15 min) and you and your friend cross (17 min).

(I have seen this before, but I did solve it on my own the first time -- honest!)
 
I was told this in a different way.

You have 3 Orcs and 3 Hobbits (anyone who has read Tolkien knows what they are) You have to cross a river. You have a boat that carries two people. One person must be in the boat for each back and forth trip. At no time can the number of Orcs out number the hobbitts becasue they will eat them. What is the lowest number of trips you can do this in? Each trip back and forth is counted.

------------------
Lee

LIfe is too important to be taken seriously. Oscar Wilde
 
I think there are two solutions:

-You and your friend cross 2 min
-you come back with torch 1 min
-two injured cross 10 min
-your friend comes back with torch 2 min
-you and your friend cross again 2 min

or

-You and your friend cross 2 min
-your friend comes back with torch 2 min
-two injured cross 10 min
-you come back with torch 1 min
-you and your friend cross again 2 min

Best,

HM

 
MichLee,

Do I count when you say "one person should be in the boat" at each cross?
Do I count when you say "max two can be in the boat?

HM
 
Yes, each way counts as one trip, and there must be one perosn in the boat eac hway. Two people max each way.

------------------
Lee

LIfe is too important to be taken seriously. Oscar Wilde
 
0. Starting state [ooohhh -- ]
1. 2 Orcs cross leaving [ohhh -- oo]
2. 1 Orc returns leaving [oohhh -- o]
3. 2 Orcs cross leaving [hhh -- ooo]
4. 1 Orc returns leaving [ohhh -- oo]
5. 2 Hobbits cross leaving [oh --hhoo]
6. 1 Hobbit & 1 Orc return [oohh - oh]
7. 2 Hobbits cross leaving [oo --hhho]
8. 1 Orc returns leaving [ooo -- hhh]
9. 2 Orcs cross leaving [o -- oohhh ]
10. 1 Orc returns leaving [oo -- ohhh]
11. 2 Orcs cross leaving [-- ooohhh ]
Which completes the crossing..

This is sort of like the Towers of Hanoi
puzzle which is a standard programming
exercise for first year Computer Science
Majors..

Good puzzle...
 
Very good.
smile.gif
and in the least number of attempts. too. Yes, there are a variet yof these same type puzzles.

------------------
Lee

LIfe is too important to be taken seriously. Oscar Wilde
 
give the light to the guy who will take 10 min. he is on the bridge and can shine it for both himself and others, sned the other guy 5 min with him. then 2 min guy adn then you, with manipulation of te light beam all will be across in about 10 min.

------------------
Sanity is overrated, simply a moonbeam spilling pearls on a dark and treacherous sea.
j . p hissom
 
Not a bad idea, asuming that the bridge is small enough to allow that. If the bridge were a long rickety one, say one of those you might see in an "Indiana Jones" type movie, it might not work. A misstep would not be worth the risk. Good thinking, though.
 
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