C++ Library for Competitive Programming
/*
* @title 数学/オイラーの $\varphi$ 関数/オイラーの $\varphi$ 関数の数表
*
* verification-helper: PROBLEM http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=NTL_1_D
*/
#include <iostream>
#include <vector>
#include "emthrm/math/euler_phi.hpp"
#include "emthrm/math/euler_phi_init.hpp"
int main() {
constexpr int M = 1000000;
const std::vector<int> ans = emthrm::euler_phi_init(M);
int n;
std::cin >> n;
std::cout << (n <= M ? ans[n] : emthrm::euler_phi(n)) << '\n';
return 0;
}
#line 1 "test/math/euler_phi_init.test.cpp"
/*
* @title 数学/オイラーの $\varphi$ 関数/オイラーの $\varphi$ 関数の数表
*
* verification-helper: PROBLEM http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=NTL_1_D
*/
#include <iostream>
#include <vector>
#line 1 "include/emthrm/math/euler_phi.hpp"
#include <cassert>
namespace emthrm {
long long euler_phi(long long n) {
assert(n >= 1);
long long res = n;
for (long long i = 2; i * i <= n; ++i) {
if (n % i == 0) [[unlikely]] {
res -= res / i;
while (n % i == 0) n /= i;
}
}
return n > 1 ? res - res / n : res;
}
} // namespace emthrm
#line 1 "include/emthrm/math/euler_phi_init.hpp"
#include <numeric>
#line 6 "include/emthrm/math/euler_phi_init.hpp"
namespace emthrm {
std::vector<int> euler_phi_init(const int n) {
std::vector<int> phi(n + 1);
std::iota(phi.begin(), phi.end(), 0);
for (int i = 2; i <= n; ++i) {
if (phi[i] == i) [[unlikely]] {
for (int j = i; j <= n; j += i) {
phi[j] -= phi[j] / i;
}
}
}
return phi;
}
} // namespace emthrm
#line 12 "test/math/euler_phi_init.test.cpp"
int main() {
constexpr int M = 1000000;
const std::vector<int> ans = emthrm::euler_phi_init(M);
int n;
std::cin >> n;
std::cout << (n <= M ? ans[n] : emthrm::euler_phi(n)) << '\n';
return 0;
}