Score : $500$ points

问题描述

给定一个字符串 $S$。可以获得多少个不同的字符串，它们是 $S$ 的非空、不必连续 子序列的排列？

由于计数可能非常大，请将结果模 $998244353$ 后输出。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

Given is a string $S$. How many different strings can be obtained as a permutation of a non-empty, not necessarily contiguous subsequence of $S$?

Since the count can be enormous, print it modulo $998244353$.

Constraints

• $S$ is a string of length $1$ and $5000$ (inclusive) consisting of lowercase English letters.

Input

Input is given from Standard Input in the following format:

$S$

Output

Print the number of different strings that can be obtained as a permutation of a subsequence of $S$, modulo $998244353$.

Sample Input 1

aab

Sample Output 1

8

There are $8$ different strings that can be obtained as a permutation of a subsequence of $S$: a, b, aa, ab, ba, aab, aba, baa.

Sample Input 2

aaa

Sample Output 2

3

Sample Input 3

abcdefghijklmnopqrstuvwxyz

Sample Output 3

149621752

Be sure to print the count modulo $998244353$.

update @ 2024/3/10 10:10:34