In a polar circuit it causes the loop current to flow in a direction opposite to that for a mark impulse.

在极性电路中，空号脉冲促使环路电流向传号脉冲相反的方向流动。

youdao

Well, this question mark becomes an O, this question mark becomes an O, and then the loop terminates 0 1 2 because it's iterating from zero to N so that's zero, 1, 2 and the length of the string is 3 so the loop terminates, but I remember that I needed to have this special sentinel value so I'm just going to put it there manually.

嗯，这个问号变成了，这个问号变成了0，然后循环结束了,以为迭代从0到N，那就是，字符串的长度是3，然后循环就结束了，但是我记得我需要这个特殊的标记值,所以需要手动的加上它。

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