When I started merging, I did merging three times across this whole board, this level, this level, and this level, and each time because of the way I was advancing my fingers I touched each number just once.

在整个过程中，我一共做了,三次合并，这一层，这一层，和这一层，而且每次,由于要前移手指，因此对每个数字,仅仅移动了一次。

哈佛公开课 - 计算机科学课程节选