Village of Demons & Sleeping Man Puzzle || Logical Interview Puzzles

Puzzle Details:

Given a village with demons and a sleeping man, the man is always sleeping and never wakes up. Now a demon can eat the sleeping man, but after that, he will fall asleep that demon will sleep after eating the man, now any demon can eat another sleeping demon.

If demons are very smart and would always choose to stay alive than to eat the man and risk their lives. so if initially there are 65 demons and 1 sleeping man... What would happen in the village??

Take your time to solve this puzzle before checking the solution. Do not forget to Share your approach in the comment section.

Solution:

one must think carefully to solve this kind of puzzle, most of the time in interviews people end up answering this question incorrectly.

The solution to such puzzles can be easily found working in the bottom-up approach:

Let's go step by step.

Consider there are only 1 demon and 1 human. 

This is a simple scenario, here demons eat humans and fall into sleep since the demon knows that nobody else is there to kill him.

Consider there are only 2 demons and 1 human.

if there are 2 demons and 1 human nothing happens. This is because if a demon eats a human and sleeps then there is one more demon that eats the sleeping demon. Since demons are logically strong and their goal is to survive in this case demons will not take the decision to eat humans.

Now Consider there are only 3 demons and 1 human.

If there are 3 demons 1 human, and one demon eats the human. This is because the demon which eats a human knows there will be only 2 demons left who are awake after he sleeps after eating a human and if there are 2 demons left none will try to eat the sleeping demon since that will risk his life.

Now Consider there are only 4 demons and 1 human.

if there are 4 demons and 1 human nothing happens. This is because if a demon eats a human and sleeps then there are three more demons waiting to eat the sleeping demon. Since demons are logically strong and their goal is to survive in this case demons will not take the decision to eat humans.

In general:

if there are an odd number of eaters and one sleeping target, one of the eaters is a demon who will eat the target that is either a sleeping demon or a man.

if eaters are even(>=2) nothing will happen because if he eats the target he will become the target, Now eaters will be odd and according to the earlier case target will be eaten, so nobody of demons wants to become the target so nobody eats.

Since there are 65 demons which is the odd number of demons and if there are the odd number of demons one demon eats the sleeping man. nothing happens after that.