BSGS，式子推对了，但是重改了无数次也没写出来……

#include<iostream>
#include<unordered_map>
#include<cmath>
using namespace std;
#define int long long

int gcd(int a, int b) { return (b == 0? a : gcd(b, a%b)); }

int quickpow(int a, int x, int p)
{
	int sum = 1, tot = a;
	while(x)
	{
		if(x & 1)
			sum = (sum * tot) % p;
		tot = (tot * tot) % p;
		x >>= 1;
	}
	return sum;
}

int inv(int k, int p)
{
	return quickpow(k, p - 2, p);
}

int BSGS(int a, int b, int p)
{
	a %= p, b %= p;
	if(b == 1)
		return 0;
	
	unordered_map <int, int> hash;
	int am = 1, ami = 1, baj = b;
	int M = ceil(sqrt(p));
	
	for(int j = 0; j < M; j ++)
		hash[baj] = j, baj = (baj * a) % p;
	am = quickpow(a, M, p);
	for(int i = 1; i <= M; i ++)
	{
		ami = (ami * am) % p;
		if(hash.count(ami))
			return i * M - hash[ami];
	}
	return -1;
}

signed main()
{
	int T;
	cin >> T;
	while(T --)
	{
		int p, a, b, x1, t;
		cin >> p >> a >> b >> x1 >> t;
		
		if(x1 == t)
		{
			cout << "1\n";
			continue;
		}
		
		if(a == 0)
		{
			cout << (b == t? 2:-1) << '\n';
			continue;
		}
		
		if(a == 1)
		{
			int w = ((t-x1) % p + p) % p;
			if(w % gcd(b, p) != 0)
			{
				cout << "-1\n";
				continue;
			}
				
			int inv_b = inv(b, p);
			cout << ( ((t-x1) * inv_b)%p + p )%p + 1 << '\n'; 			
		}
		
		int inv_a_1, inv_fm, y, ans;
		
		inv_a_1 = inv(a-1, p);
		inv_fm = inv((x1 + (b*inv_a_1)%p) % p, p);
		
		ans = BSGS(a, ( ( (t + (b*inv_a_1)%p)%p ) * (inv_fm%p) )% p, p);
		cout << (ans == -1? ans : ans+1) << '\n';
	}
	return 0;
}