【BZOJ】【P3239】【Discrete Logging】【题解】【BSGS】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=3239

裸题

Code:

#include<bits/stdc++.h>using namespace std;typedef long long LL;LL p,a,b;LL pw(LL x,LL k,LL p){LL ans=1;for(;k;k>>=1){if(k&1)ans=(ans*x)%p;x=(x*x)%p;}return ans;} void solve(){a%=p;b%=p;map<LL,LL>hash;LL m=ceil(sqrt(p)),am=pw(a,m,p),v=pw(a,p-2,p),e=1;hash[b]=0;for(int i=1;i<=m;i++)if(!hash.count(b*v%p))hash[(b*=v)%=p]=i;//cout<<b<<" ";cout<<endl;for(int i=0;i<=m;i++){if(hash.count(e)){cout<<i*m+hash[e]<<endl;return;}e=e*am%p;}puts("no solution");}int main(){while(cin>>p>>a>>b)solve();return 0;}