BOJ 5636 - 소수 부분 문자열 [C++]

문제

링크

풀이

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
 
vector<bool> sieve(int n) {
  vector<bool> prime(n+1, true);
  prime[0] = prime[1] = false;
  for (int i=4; i<=n; i+=2) {
    prime[i] = false;
  }
  for (int i=3; i*i<=n; i+=2) {
    if (!prime[i]) continue;
    for (int j=i*i; j<=n; j+=i*2) {
      prime[j] = false;
    }
  }
  return prime;
}
 
bool solve(const vector<bool> &p) {
  string s; cin >> s;
  if (s == "0") return false;
 
  int ans = 0;
  for (int i=1; i<=5; i++) {
    for (int j=0; j+i<s.length(); j++) {
      int n = stoi(s.substr(j, i));
      if (p[n]) ans = max(ans, n);
    }
  }
  cout << ans << "\n";
 
  return true;
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  vector<bool> p = sieve(100000);
  while (solve(p));
  return 0;
}