Cod sursa(job #2289430)

Utilizator alexbuzescuAlexandru Buzescu alexbuzescu Data 24 noiembrie 2018 16:32:36
Problema Invers modular Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.97 kb
#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("inversmodular.in");
ofstream fout("inversmodular.out");
long long a,n;
long long ridicare(long long baza,long long exp){
    long long rez=1;
    while(exp!=0){
        if(exp%2==0){
            baza=(baza*baza)%n;
            exp/=2;
        }
        else{
            rez=(rez*baza)%n;
            exp--;
        }
    }
    return rez;
}
bool IsPrime(){
    for(long long i=2;i*i<=n;i++){
        if(n%i==0)return false;
    }
    return true;
}
int main()
{
    fin>>a>>n;
    if(IsPrime()){
    fout<<ridicare(a,n-2)%n;
    }
    else{
        long long phi=n,cn=n,d=2;
        while(cn!=1){
            bool ok=false;
            while(cn%d==0){
                cn/=d;
                ok=true;
            }
            if(ok){
                phi=phi-phi/d;
            }
            d++;
        }
        fout<<ridicare(a,phi-1)%n;
    }

    return 0;
}