一个字符串为完美回文等价于其所有字符相同,枚举最后字符串的字符 ccc ,修改次数即为 n−cntcn-cnt_cn−cntc ,我们要最小化修改次数, nnn 为定值,因此就要最大化 cntccnt_ccntc,找出出现次数最多的字符的出现次数后用 nnn 减一减就好了。
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