使用快速幂，分配乘法、BSGS

最后两点Wa了

#include<iostream>
#include<map>
#include<cmath>
#include<vector>
#define ll unsigned long long
//104858563
using namespace std;
inline ll mult(ll a,ll b,ll p){
	ll L=a*(b>>32)%p*(1ll<<32)%p;
	ll R=a*(b&((1ll<<32)-1))%p;
	return (L+R)%p;
}
template<class T>
inline T qpow(T a,T b,T p){
	if(b==0)return 1;
	T tmp,base=a;
	tmp=1;
	while(b!=0){
		if(b&1){
			tmp*=base;
			tmp%=p;
		}
		base*=base;
		base%=p;
		b>>=1;
	}
	return tmp;
}
int main(){
	ll k,m,s;
	map<ll,int>re;
	vector<bool>err;
	cin>>k>>m;
	s=ceil(sqrt(m))+1;
    ll tmp=mult(9,k,m)+1,num=1,lin=1,at=1;
    re[tmp]=0;
    for(int B=1;B<=s;B++){
    	num=mult(10,num,m);
    	re[mult(tmp,num,m)]=B;
	}
	auto ke=re.find(1);
	if(ke!=re.end()&&ke->second==0){
		cout<<0;
		return 0;
	}
	else
		at=lin=qpow((ll)10,s,m);
	for(int A=1;A<=s;A++){
		if((ke=re.find(at))!=re.end()){
			if(A*s-ke->second<0)cout<<err[4];
			cout<<A*s-ke->second;
			return 0;
		}
		at=mult(lin,at,m);
	}
	return 0;
}