BOJ 4355 - 서로소 [C++]

문제

링크

풀이

#include <iostream>
using namespace std;
 
int phi(int n) {
  int ret = n;
  for (int i=2; i*i<=n; ++i) {
    if (n % i) continue;
    ret -= ret / i;
    while (!(n % i)) n /= i;
  }
  if (n > 1) ret -= ret / n;
  return ret;
}
 
bool solve(void) {
  int n; cin >> n;
  if (n == 0) return false;
 
  cout << (n == 1 ? 0 : phi(n)) << "\n";
  return true;
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  while (solve());
  return 0;
}