Brainteasers are logic puzzles. Used to test analytical and problem-solving ability
Brainteasers or Logic puzzles are a very popular part of interviews especially within the IT & Communications industry. They serve as a platform to demonstrate the interviewee’s creativity, analytical skills and ability to think, "out-of-the-box."
Even if they don't come up with the right answer as long as they let you know what they are thinking as they attack the question. You can judge their analytical ability and to showcase an individual's creativity.
Amazon asks, "How many gas stations are there in the United States?"
This is a stat that most people do not know; it’s how they’d come to the answer that is most important.
Instead of finding out how good a candidate is at studying this will highlight a candidates thinking strength.
Logic puzzles or Brainteaser cases can take many forms. Some are straightforward logic puzzles (for example, "If you have a drawer filled with eight white socks and 13 black socks, what is the smallest number you would have to pull out without looking in order to be sure that you had a matching pair?").
Other questions might not have a single correct answer. Instead, For example, you may ask to list all the ways they could find a needle in a haystack.
Sample Brainteaser 1
You have eight balls, one of which is heavier than the others. All the balls appear identical. You have a balance-type scale, and you can perform trials on the balls. What is the minimum number of trials required to determine which is the heaviest ball?
Solution
Two. You start by putting three balls on each side of the scale. There are two basic outcomes: one set of three is heavier, or both sets are in balance. If one set is heavier, you choose two balls from that set and weigh one on each side of the balance. If the balls balance, you know that the remaining one from the set is the heavy one.
In the second outcome from the first measurement, the two sets of three balls are in balance. That means the heavy ball is among the remaining two. Weigh them, and you'll have your answer.
Sample Brainteaser 2
Imagine two adjoining rooms that are connected by a CLOSED door. You are standing in one of those rooms with three light switches in front of you (initially in the OFF position). In the next room, there are three ordinary 60 watt light bulbs. Your job is to figure out which light switch corresponds to which light bulb. The constraint is:
You can only open the door into the other room (with the light bulbs) ONCE. Once you open the door, you can not operate the switches again.
Solution
Turn the first switch on, and leave that bulb on.
Turn the second switch on, leave it on for five min, then turn it off.
Go into the room quickly -- the light that is on was the first switch. then touch the other two bulbs -- the one that is warm to touch is the second switch, and the one that is cool to touch is the third switch.
Sample Brainteaser 3
You have two blocks of incense, each of which burns for one hour. These blocks of incense are very strange and have a non-uniform density: You could light the block and have the first 10% take 50 minutes to burn and the last 90% burn in 10 minutes, for example. Thus, dividing the block in any way makes it impossible to tell how long each of the parts will last.
Unfortunately, you are asked to precisely measure 45 minutes of time. How do you do it?
Solution
Light the first stick at both ends and the second stick at only one end. The first stick will burn out in half an hour. Then, there is exactly one half hour of burning left in the other stick, so light the other end. It will burn out in fifteen minutes.
Sample Brainteaser 4
You have 12 coins and all but one are the same weight. You have a counter balance and you are allowed to run three trials. You have to determine which coin is a different weight, and whether it is heavier or lighter than the other coins.
Solution
Here's the solution, in 3 steps or less.
1) Put six on either side of the scale. The side that is heavier (or lighter, depending on what the bad coin is) contains the coin
2) Of these six coins, put 3 on either side, and repeat, as in step 1
3) Of these three coins, put one on one side, and a second on the other side. If they are unbalanced, you know which one is the bad coin. If they balance perfectly, the third coin is the one.
Sample Brainteaser 5
There is a bridge over a canyon. You are on one side with a fox, a hen and some grain. If you leave the fox alone with the hen, he will eat her and if you leave the hen alone with the grain, she will eat it. You can only take one item at a time across the bridge. How do you get all three to the other side?
Solution
-> he and hen
<- he
-> he and fox
<- he and hen
-> he and grain
<- he
-> he and hen
Sample Brainteaser 6
A man is trapped in a room. The room has only two possible exits: two doors. Through the first door there is a room constructed from magnifying glass. The blazing hot sun instantly fries anything or anyone that enters. Through the second door there is a fire-breathing dragon. How does the man escape?
Solution
He waits until night time and then goes through the first door.