Cod sursa(job #2675265)

Utilizator AlexMariMarinescu Alexandru AlexMari Data 21 noiembrie 2020 11:46:41
Problema Invers modular Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.8 kb
#include<bits/stdc++.h>
using namespace std;
ifstream fin("inversmodular.in");
ofstream fout("inversmodular.out");


int n,a,phi;

int phi_euler(int nr)
{
    int i,phii=nr;
    for(i=2; i*i<=nr; i++)
    {
        if(nr%i==0)
        {
            phii/=i;
            phii*=(i-1);
            while(nr%i==0)
                nr=nr/i;
        }
    }
    if(nr!=1)//ins ca a ramas un nr prim
    {
        phii/=nr;
        phii*=(nr-1);
    }
    return phii;
}

int lgput(int base,int exp)
{
    long long i;
    int aux=base,ans=1;
    for(i=1; i<=exp; i*=2)
    {
        if(i&exp)
            ans=(1LL*ans*aux)%n;
        aux=(1LL*aux*aux)%n;
    }
    return ans;
}

int main()
{
    fin>>a>>n;
    phi=phi_euler(n);
    fout<<lgput(a,phi-1);
    return 0;
}