BOJ 2061 - 좋은 암호 [C++]

문제

링크

풀이

#include <iostream>
#include <string>
#include <vector>
using namespace std;
 
vector<bool> precompute(void) {
  vector<bool> prime(1000001, true);
  prime[0] = prime[1] = false;
  for (int i=4; i<=1000000; i+=2) {
    prime[i] = false;
  }
 
  for (int i=3; i*i<=1000000; i+=2) {
    if (!prime[i]) continue;
    for (int j=i*i; j<=1000000; j+=i*2) {
      prime[j] = false;
    }
  }
  return prime;
}
 
void solve(vector<bool>& prime) {
  string k; int l; cin >> k >> l;
 
  for (int i=2; i<l; i++) {
    if (!prime[i]) continue;
    int r = 0;
    for (char c : k) r = (10 * r + (c - '0')) % i;
    if (r) continue;
    cout << "BAD " << i;
    return;
  }
  cout << "GOOD";
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  vector<bool> prime = precompute();
  solve(prime);
  return 0;
}