Problem I am trying to solve is this:
There are n nodes, and for every pair of node $X$ and $Y$, the relation "$X \space knows \space Y$" is either $T$ or $F$. It is possible that "$X \space knows \space Y$" but "$Y \space doesn't \space know \space X$".
We are trying to find if a special node exists: that is known to everyone but doesn't know anyone. How can you find out if such node exists by using only this type of query: For any nodes $X$ and $Y$, ask $X$ "$if \space X \space knows \space Y$". This query can be asked unlimited amount of times, but the total number of queries should be $O(n)$. I can think of $O(n^2)$ case but how to do it with $O(n)$ queries? Thanks!