returns 216. There are 216 different possibilities to put a sequence of 3 playing cards together out of six playing cards if every card is returned before the next one is drawn.
返回 216。在 6 张扑克牌中抽出三张排列，并且每抽出一张后，在抽第二张之前再把这张放回牌中，这时可能的排列共有 216 种。