To see how the cards above form a set, take each characteristic in turn.First, each card has different symbol: the first card has squiggles, the second diamonds, and the third ovals.

• 1：本题的思路一是比较普通的，也很好想，对本题也能通过，在这种情况下我们不妨想想能否有进一步改进效率的可能。