All of a sudden a third element has been injected in to the comparison.

突然第三个元素又跃入眼帘了。

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And one is the third element. And just return, it's done. It is a palindrome. That make sense.

完成，数组时回文的，这就对了，因为数组1a1从前面和从后面读都是一样的。

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