Cod sursa(job #1647635)

Utilizator Vlad_lsc2008Lungu Vlad Vlad_lsc2008 Data 10 martie 2016 21:26:41
Problema Invers modular Scor 50
Compilator cpp Status done
Runda Arhiva educationala Marime 0.7 kb
#include<cstdio>
#include<iostream>
#define ll long long
using namespace std;

ll n,a;

ll getphi(ll numar)
{
    int nr=numar,var,sol=numar;
    for(int i=2;i*i<=numar;i++)
        if(nr%i==0)
        {
            var=0;
            while(nr%i==0) nr/=i;
            sol=(sol/i)*(i-1)%n;
        }
    if(nr>1)
    {
        sol=(sol/nr)*(nr-1)%n;
    }
    return sol;
}

int main()
{
    freopen("inversmodular.in","r",stdin);
    freopen("inversmodular.out","w",stdout);
    scanf("%lld%lld",&a,&n);
    ll p=getphi(n)-1;
    ll sol=1;
    for(int i=0; (1<<i)<=p; i++)
    {
        if( (1<<i)&p ) sol=sol*a%n;
        a=a*a%n;
    }
    cout<<sol<<'\n';
    return 0;
}