秋招模拟赛第39场|2023.09.02-淘天-研发
- Status
- Done
- Rule
- IOI
- Problem
- 3
- Start at
- 2023-9-6 19:00
- End at
- 2023-9-6 20:12
- Duration
- 1.2 hour(s)
- Host
- Partic.
- 25
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塔子哥最近做了很多字符串的题目,普通的字符串题已经难不倒他了!
但是这次他遇到了一个难题:给定一个字符串,有多少子序列满足首尾字符是相同的?
注:子序列可以不连续,但是需要保证在原串中的顺序。
一个字符串,仅由小写字母组成,字符串长度不大于100000。
满足条件的子序列的数量。由于答案过大,请将答案对于998244353取模
输入
abca
输出
8
说明
长度为1的子序列均符合要求,共4个。
长度为2的子序列,有"ab","ac","aa","bc","ba","ca",符合条件的有"aa"。
长度为3的子序列,有"abc","aba","aca","bca",符合条件的有"aba","aca"。
长度为4的子序列,有"abca",符合条件的有"abca"。
答案为4+1+2+1=8
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