| № | Пользователь | Рейтинг |
|---|---|---|
| 1 | tourist | 3993 |
| 2 | jiangly | 3743 |
| 3 | orzdevinwang | 3707 |
| 4 | Radewoosh | 3627 |
| 5 | jqdai0815 | 3620 |
| 6 | Benq | 3564 |
| 7 | Kevin114514 | 3443 |
| 8 | ksun48 | 3434 |
| 9 | Rewinding | 3397 |
| 10 | Um_nik | 3396 |
| Страны | Города | Организации | Всё → |
| № | Пользователь | Вклад |
|---|---|---|
| 1 | cry | 167 |
| 2 | Um_nik | 163 |
| 3 | maomao90 | 162 |
| 3 | atcoder_official | 162 |
| 5 | adamant | 159 |
| 6 | -is-this-fft- | 158 |
| 7 | awoo | 155 |
| 8 | TheScrasse | 154 |
| 9 | Dominater069 | 153 |
| 10 | djm03178 | 152 |
Here is the link — http://codeforces.me/problemset/problem/559/C This is similar to this — https://www.codechef.com/CDCRF15R/problems/CWAYS/
In the solutions, I can see inverse factorial being calculated as
inv(n) = pow(n,mod-2)
I don't get where the mod-2 value comes from. Can someone please explain?
This is because pow(n, p - 1) = 1(modp) holds (Fermat's Little Theorem).
So pow(n, p - 2) * n = 1(modp) also holds, and it means inv(n) = pow(n, p - 2).
Due to Fermat's little theorem, if p = 109 + 7 is prime then
Unable to parse markup [type=CF_TEX]
.