Summer, Autumn and Winter are playing chess and each will have a match with the other two. Now, Summer has played 2 matches and Autumn has played 1 match. How many matches has Winter played?
We can see that Summer has played both of them, so Winter has played at least one match. However, Winter hasnt played Autumn yet, since shes played only once. Thus, Winter has played just one match.
The key here is to start with the player about whom you know the mostif you know that someone has already played all his/her matches, e.g., start there.
Then apply what you learn from that player to get other info about the other players, and repeat this process until you know everything.