Cod sursa(job #2467830)

Utilizator TudolHulubei Tudor Tudol Data 5 octombrie 2019 08:53:41
Problema Invers modular Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.73 kb
#include <bits/stdc++.h>
using namespace std;

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


int phi(int n)
{
    ///complexitate O(sqrt(n))

    int sol = n, p;
    for(p = 2; p * p <= n && n > 1; 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 lgput(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 a, n;

int main()
{
    in >> a >> n;
    out << (lgput(a, (phi(n) - 1), n));
    return 0;
}