洛谷 3811 【模板】乘法逆元

非常想三种方法都用一下，于是rand()走起：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
int n, p, y, x;
int inv[3000200];
void write(int x)
{
    if (x < 0) putchar('-'), x = -x;
    if (x > 9) write(x / 10); putchar(x % 10 ^ 48);
}
void ex_gcd(int a, int b)
{
    if (!b)
    {
        x = 1, y = 0;
        return;
    }
    ex_gcd(b, a % b);
    int t = x;
    x = y;
    y = t - a/b * y;
    return;
}
int fastpow(int a, int b)
{
    int ans = 1;
    while (b)
    {
        if (b & 1) ans = (1LL * ans * a) % p;
        b >>= 1, a = (1LL * a * a) % p;
    }
    return ans;
}
int main()
{ 
    srand(time(0));
    scanf("%d%d", &n, &p);
    inv[1] = 1;
    for (register int i = 2, j = rand() % 30; i <= n; ++i, j = rand() % 30)
        if (j != 1 && j != 2) inv[i] = 1LL * inv[p % i] * (p - p / i) % p;
        else if (j == 1) ex_gcd(i, p), inv[i] = x, inv[i] = (inv[i] % p + p) % p;
        else if (j == 2) inv[i] = fastpow(i, p - 2);
    for (register int i = 1; i <= n; ++i) 
        write(inv[i]), putchar('
');
    return 0;
}