There are N people in a room and one of them is a celebrity. In the room everyone knows the celebrity and celebrity doesn’t know anyone in the room. You have 1 question ‘do you know him?’ and you can ask this question N times to anyone in the room. The person to whom you are asking question will reply ‘Yes, I know this guy’ or ‘No, I don’t know this guy’. By asking the same question N times to whoever you want to ask you have to figure out who is celebrity in the room. If A knows B doesn’t mean B knows A.
You can find well detailed solution of this problem on the internet but i would like to share the solution with you …
Let us consider that you have N person numbered from 1 to N inclusively and you have only one question to ask A knows B …
Pick up any two person … from the N persons
Lets us say we have picked person number 1 and 2 .(you can pick any two of your choice it will not affect the solution at all).
Two possibilities .
1. 1 knows 2 = True Here you can see 1 knows 2 if 1 would have been a celebrity than this should be false . It means 1 is not a celebrity .. you are now left with only N1 person . 2. 1 knows 2 = false if this is the case we can claim that 2 is not celebrity because if 2 would have been a celebrity then 1 must know 2 . Here again you are now left with N1 person.
By asking 1 question you can remove 1 person . you have to ask N1 questions and you will end up finding the celebrity …
Cheers codechef
Wishing you a very happy new year
You can find more solution and discussion about this problem over this page …
 Take 1 person and ask whether he knows other persons, one by one upto (N1). But once you are getting answer YES. Stop there. Lets say this person is m. Now remove person1 from the list.
 Take m and ask the same Q. If he’s saying he doesn’t know anyone, then m is the celebrity.
In step 1 if you are getting all No… then that person 1 is the celebrity.
In step 2 if you are getting answer YES, then consider that person is n.
Now eliminate m and take n and do the same step.
Hello subrat2014
You have not the read the question carefully please read the question again you are only allow to ask this question N times …

Take 1 person and ask whether he knows other persons, one by one upto (N1). But once you are getting answer YES. Stop there. Lets say this person is m. Now remove all the persons before m including person 1 from the list.
If m is the last candidate, then he is the celebrity.
3. if m is not last candidate,
Take m and ask the same Q.
If he’s saying he doesn’t know anyone, then m is the celebrity.
In step 1 if you are getting all No… then that person 1 is the celebrity.
In step 3 if you are getting answer YES,
then repeat the step1
Updated the logic.
nice answer…
hey @ma5termind can you tell where can we find more such interview problems, because this one sounds interesting…
Can you mention links here??
Thank you…