Palindromic Equivalence
题目描述
给出一个由小写字母组成的字符串S，问有多少由小写字母
构成的字条串S',满足
1:|S|'=|S|
2:S'[L..R]是回文串，当且仅当S[L..R]是回文串
输入格式
一个字符串S,长度<=10^6
输出格式
输出答案Mod10^9+7
abba
650 Only words of the form xyyx are palindromically equivalent to abba, where x and y are distinct letters. The English alphabet contains 26 letters, consequently there are 26*25=650 such words in total.