求原根模版

#include <cstdio>
#include <cstring>
using namespace std;
typedef long long LL;
int p[100000], c;

LL pow_mod(LL a, LL x, LL m)
{
	LL ans = 1;
	while(x)
	{
		if(x&1)
			ans = ans * a % m;
		a = a * a % m;
		x >>= 1;
	}
	return ans;
}

bool ok(int x, int ph, int m)
{
	for(int i = 0; i < c; i++)
		if(pow_mod(x, ph/p[i], m) == 1)
			return false;
	return true;
}
void divide(int x)
{
	c = 0;
	for(int i = 2; i*i <= x; i++)
	{
		if(x % i == 0)
		{
			p[c++] = i;
			while(x % i == 0)
				x /= i;
		}
	}
	if(x > 1)
		p[c++] = x;
}
int main()
{
	int T;
	scanf("%d", &T);
	while(T--)
	{
		int n;
		scanf("%d", &n);
		int m = n, ans = m;
		for(int i = 2; i*i <= n; i++)
		{
			if(n%i == 0)
			{
				ans = ans / i * (i-1);
				while(n%i == 0)
					n /= i;
			}
		}
		if(n > 1)
			ans = ans / n * (n-1);
		//printf("%d\n", ans);
		divide(ans);
		int x = ans;
		while(!ok(x, ans, m))
			x--;
		printf("%d\n", x);
	}
	return 0;
}