Mr. S, Mr. P and Mr. Q know that there are 16 playing cards in the drawer of the desk:

Hearts A, Q, 4, spades J, 8, 4, 2, 7, 3, flowers K, Q, 5, 4, 6, and diamonds A and 5 are known.

Because Mr. P: I don't know this card. So, this card is a multi-color card, maybe 4, Q, 5, A.

Because Mr. Q: I know you don't know this card. Therefore, this card has many colors, namely hearts and diamonds.

Because Mr. P: Now I know this card. So, rule out A, because if it is A, Mr. P is still not sure about the suit.

Because Mr. Q: I also know. Therefore, Mr. Q knows only two colors, because you can definitely determine the card after excluding point A, so it is square 5.

Nature:

The puzzle between Mr. S and Mr. P was put forward by McCarthy of Stanford University. In fact, it is a reasoning problem. Under the clear definition of the topic, in order to get the result, a series of examples are proved and excluded, so as to get the answer to the question in speculation. This puzzle teaches us the way of thinking from another side.

When explaining a larger thing, people sum up and generalize various universal principles or principles from individual and special things, and then they can draw conclusions about individual things from these principles and principles.