在合并时，我的左手手指，和右手手指来回地在黑板上移动，但对每个数字只会碰到一次。

That's the finger thing from left finger to right finger going back and forth across the board, never touching a number more than once.

youdao

在合并时，我的左手手指，和右手手指来回地在黑板上移动，但对每个数字只会碰到一次。

That's the finger thing from left finger to right finger going back and forth across the board, never touching a number more than once.

youdao