Cod sursa(job #1118992)

Utilizator YoYoxxIftimesei Ioan YoYoxx Data 24 februarie 2014 14:18:23
Problema Invers modular Scor 10
Compilator cpp Status done
Runda Arhiva educationala Marime 0.88 kb
#include <fstream>
#include<math.h>
using namespace std;
ifstream in("inversmodular.in");
ofstream out("inversmodular.out");
long long a,n;
int x[2000002];

void ciur()
{
    int i,j;
    for(i=2;i*i<=n;i++)
    {
        for(j=2;j*i<=n&&x[i]==0;j++)
        {
            x[i*j]=1;
        }
    }
}

int ex(int a,int p)
{
    int sol=1,i;
    for(i=0;(1<<i)<=p;i++)
    {
        if( ((1<<i)&p)>0  ) sol=(sol*a)%n;
        a=(a*a)%n;
    }
    return sol;
}

int main()
{
    int i,nr=0,nn,j;
    in>>a>>n;
    nn=n-1;

    for(i=2;i*i<=n;i++)
    {
        if(n%i==0&&x[i]==0)
        {
            nr=n/i;
            for(j=2;j*i<=n;j++)
            {
                if(x[i*j]==0) x[i*j]=1;
                else nr--;
            }
        nn=nn-nr;
        }
    }
    if(nn==n-1)out<<ex(a,n-2);
    else out<<ex(a,nn);
    return 0;
}