Once each time. Right? I only do one swap potentially, it-- though not one potentially, each time at the end of the loop I do a swap.

每次循环做一次，对么？我其实,就可能做了一次交换，也许并不是可能，每次循环的结束我都得做一次交换。

麻省理工公开课 - 计算机科学及编程导论课程节选

For example, the stock market crash of 1929 is repeatedly re-expected even though it only happened once; it's just prominent in our thinking.

929年股市崩盘,就被反复提及,尽管这只发生过一次,但是人们对它影响深刻

耶鲁公开课 - 金融市场课程节选