Cod sursa(job #2467829)

Utilizator Rares5000Baciu Rares Rares5000 Data 5 octombrie 2019 08:53:31
Problema Invers modular Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.71 kb
#include <bits/stdc++.h>

using namespace std;

ifstream fin("inversmodular.in");
ofstream fout("inversmodular.out");

/**
Phi(n)=n*(p1-1)*(p2-1)*...*(pk-1)/(p1*p2*p3*...*pk)
*/

int Phi(int n)
{
    int p,sol;
    sol=n;
    for(p=2;n>1 && p*p<=n;p++)
    {
        if(n%p==0)
        {
            sol=sol/p*(p-1);
            while(n%p==0)
                n/=p;
        }
    }
    if(n>1) sol=sol/n*(n-1);
    return sol;
}

int LogP(int a,int n,int MOD)
{
    int p=1;
    while(n>0)
    {
        if(n%2==1) p=1LL*p*a%MOD;
        n/=2;
        a=1LL*a*a%MOD;
    }
    return p;
}

int main()
{
    int a,n;
    fin>>a>>n;
    fout<<LogP(a,Phi(n)-1,n);
    return 0;
}