质数筛法 简单版

#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

const int MAXN = 10001;

vector<int> prime;
bool isPrime[MAXN];

void Initial() {
  for (int i = 0; i < MAXN; ++i) {
    isPrime[i] = true;
  }
  isPrime[0] = false;
  isPrime[1] = false;
  for (int i = 2; i < MAXN; ++i) {
    if (!isPrime[i]) {
      continue;
    } 
    prime.push_back(i);
    for (int j = i * i; j < MAXN; j += i) {
      isPrime[j] = false;
    }
  }
  return ;
}

int main() {
  Initial();
  int n;
  while (scanf("%d", &n) != EOF) {
    bool isOutput = false;
    for (int i = 0; i < prime.size() && prime[i] < n; ++i) {
      if (prime[i] % 10 == 1) {
        isOutput = true;
        printf("%d ", prime[i]);
      }
    }
    if (!isOutput) {
      printf("-1");
    }
    printf("\n");
  }
  return 0;
}