| # | User | Rating |
|---|---|---|
| 1 | tourist | 3985 |
| 2 | jiangly | 3814 |
| 3 | jqdai0815 | 3682 |
| 4 | Benq | 3529 |
| 5 | orzdevinwang | 3526 |
| 6 | ksun48 | 3517 |
| 7 | Radewoosh | 3410 |
| 8 | hos.lyric | 3399 |
| 9 | ecnerwala | 3392 |
| 9 | Um_nik | 3392 |
| # | User | Contrib. |
|---|---|---|
| 1 | cry | 169 |
| 2 | maomao90 | 162 |
| 2 | Um_nik | 162 |
| 4 | atcoder_official | 161 |
| 5 | djm03178 | 158 |
| 6 | -is-this-fft- | 157 |
| 7 | adamant | 155 |
| 8 | awoo | 154 |
| 8 | Dominater069 | 154 |
| 10 | luogu_official | 150 |
Hi everyone!
I'm really facing problems in when to use modular inverse. I know that you should use it when calculating the following
(a / b)%p = (a * bp - 2)%p [Only when p is prime]
I know there is a case when subtracting, but I don't know how you do it exactly, can you tell me how? And are there any other cases?
Thanks in advance.
Remember, the modular inverse of some number a modulo m, is a number b such that:
a·b ≡ 1 (mod m)
That's why you use it when you have to do divisions modulo some number
.
However, a number a has inverse modulo m iff they are coprime (gcd(a, m) = 1)
If m is prime, you can apply the formula you mentioned in your post. Otherwise, you have to find the modular inverse using another method (for example, Extended GCD)
I don't know what do you mean with "case when subtracting". If you have to perform a subtraction between two numbers modulo m, there's no need to use the modular inverse.