I spotted an error here, I could have spotted it by running it on different test sets, and using prints things, another way of doing it, but this idea of at least simulating it on simple examples lets you check a couple of important questions.

操作么？我在这里发现了一个错误,我也可以通过运行不同的测试集，或者运用print声明来发现这个错误，但是至少应该用简单的例子来手工模拟下,代码的思想可以让你,对一些很重要的问题进行检验。

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