用奇偶性分析，一開始是奇數個+，偶數個-，一次無論反轉奇數個+成-，還是反轉偶數個+成-，結果還是奇數個+，偶數個-。

來源: 羅擊於 2023-11-02 21:31:43 [舊帖] [給我悄悄話] 本文已被閱讀：次

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