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先预处理出来比小于等于n的素数的个数和回文数的个数…

比赛的时候想到了是dp搞… 不过dp废…..

因为字母的排列顺序是任意的,所以判断能否形成回文串的条件就成了出现次数为奇数的字母的个数是否大于1个,如果是,那么一定不能形成回文串,否则一定可以.

C. Replacement time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Daniel has a string s, consisting of lowercase English letters and period signs (characters ‘.’). Let’s define the operation of replacement as the following sequence of steps: find a substring “..” (two consecutive periods) in string s, of all occurrences of the substring let’s choose the first one, and replace this substring with string “.”. In other words, during the replacement operation, the first two consecutive periods are replaced by one. If string s contains no two consecutive periods, then nothing happens.

啊啊啊，为什么这么弱 啥都不会呜呜呜 肿么办肿么办肿么办 不会的好多啊。。。。。