BZOJ5296 [CQOI2018] 破解D-H协议 【数学】【BSGS】

题目分析：

　　裸题。

代码：

　

 #include<bits/stdc++.h>
 using namespace std;

 typedef long long ll;

 const int BASE = ;

 #define mp make_pair

 ll g,p;
 ll srt = ;
 vector<pair<int,ll> > hash[];

 ll fast_pow(ll now,ll pw){
     if(pw == ) return now;
     ll z = fast_pow(now,pw/);
     z *= z ; z %= p;
     if(pw & )z *= now,z %= p;
     return z;
 }

 void CreatHash(){
     ll xm = fast_pow(g,srt);
     ll hh = xm;
     for(ll i=;(i-)*srt<=INT_MAX;i++,hh = (hh*xm)%p){
     hash[hh % BASE].push_back(mp(i,hh));
     }
 }

 void read(){
     scanf("%lld%lld",&g,&p);
     CreatHash();
 }

 ll solve(ll now){
     ll hh = g;
     for(int i=;i<=;i++,hh=(hh*g)%p){
     ll nowp = (hh*now)%p;
     for(int j=;j<hash[nowp%BASE].size();j++){
         ll out = hash[nowp%BASE][j].second;
         if(out == nowp){
         out = hash[nowp%BASE][j].first;
         return out*srt-i;
         }
     }
     }
 }

 void work(){
     int n;scanf("%d",&n);
     for(int i=;i<=n;i++){
     ll a,b; scanf("%lld%lld",&a,&b);
     ll hh = solve(a);
     ll key = fast_pow(b,hh);
     printf("%lld\n",key);
     }
 }

 int main(){
     read();
     work();
     return ;
 }