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

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

裸题

Code:

#include
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;
	maphash;
	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<>p>>a>>b)
	solve();
	return 0;
}