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给新手解释下答案

Posted by fbixiaozc135 at 2007-07-16 20:30:30 on Problem 3210
 因为当coins全部同向时,最后要同向必然要翻转偶数次,所以若有偶数个coins时,若只有一个跟其他的反向时,必要翻转奇数次以达到目的。这两种情况矛盾,所以,偶数时题无解,对于奇数个coin,可由数学归纳法得到结果。

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