bzoj2242: [SDOI2011]计算器（BSGS）

http://www.lydsy.com/JudgeOnline/problem.php?id=2242

 

#include<map>
#include<cmath>
#include<cstdio>

using namespace std;

int y,z,p;

map<int,int>mp;

int Pow(int a,int b,int m)
{
    int ans=1;
    for(;b;a=1LL*a*a%m,b>>=1)
        if(b&1) ans=1LL*ans*a%m;
    return ans;
}

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

void exgcd(int a,int b,long long &x,long long &y)
{
    if(!b) { x=1; y=0; return; }
    exgcd(b,a%b,y,x); y-=a/b*x;
}

void bsgs()
{
    mp.clear();
    int m=ceil(sqrt(p));
    int mul=z;
    //mp[z]=0;
    for(int j=1;j<=m;++j)
    {
        mul=1LL*y*mul%p;
        mp[mul]=j;
    }
    int am=Pow(y,m,p);
    mul=1;
    for(int j=1;j<=m;++j)
    {
        mul=1LL*mul*am%p;
        if(mp.find(mul)!=mp.end()) 
        {
            printf("%d\n",j*m-mp[mul]);
            return;
        }
    }
    puts("Orz, I cannot find x!");
}    

int main()
{
    int T,k;
    scanf("%d%d",&T,&k);
    if(k==1)
        while(T--)
        {
            scanf("%d%d%d",&y,&z,&p);
            printf("%d\n",Pow(y,z,p));
        }
    else if(k==2)
    {
        long long x0,y0;
        int g;
        while(T--)
        {
            scanf("%d%d%d",&y,&z,&p);
            g=gcd(y,p);
            if(z%g) puts("Orz, I cannot find x!");
            else
            {
                y/=g; p/=g;
                exgcd(y,p,x0,y0);
                x0=(x0%p+p)%p;
                x0=x0*z/g%p;
                printf("%lld\n",x0);
            }
        }
    }
    else
        while(T--)
        {
            scanf("%d%d%d",&y,&z,&p);
            if(!(y%p)) puts("Orz, I cannot find x!");
            else bsgs();
        }
    return 0;
}