Score : $300$ points

问题描述

给定一个字符串 $S$。

有多少种方法可以选择并以从左到右的顺序下划线其八个字符，使得这些字符拼出 c, h, o, k, u, d, a, i？

由于计数可能会非常庞大，请将结果模 $(10^9 + 7)$ 后输出。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

You are given a string $S$.
How many ways are there to choose and underline eight of its characters so that those characters read c, h, o, k, u, d, a, i from left to right?
Since the count can be enormous, print it modulo $(10^9 + 7)$.

Constraints

• $8 \leq |S| \leq 10^5$
• $S$ consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

$S$

Output

Print the number of ways modulo $(10^9 + 7)$.

Sample Input 1

chchokudai

Sample Output 1

3

We have three valid ways:

chchokudai
chchokudai
chchokudai

while the following is invalid:

chchokudai

Sample Input 2

atcoderrr

Sample Output 2

0

The answer may be $0$.

Sample Input 3

chokudaichokudaichokudai

Sample Output 3

45

update @ 2024/3/10 09:25:47