题解 | #素数#

//土尔逊Torson 编写于2023/5/08
#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

const int MAXN = 10001;

vector<int> prime;   //保存质数
bool isPrime[MAXN];  //标记数组

void Initial() {
	for (int i = 0; i < MAXN; ++i) {    //初始化
		isPrime[i] = true;
	}
	isPrime[0] = false;
	isPrime[1] = false;
	for (int i = 2; i < MAXN; ++i) {
		if (!isPrime[i]) {              //非质数则跳过
			continue;
		}
		prime.push_back(i);
		for (int j = i*i; j < MAXN; j += i) {
			isPrime[j] = false;         //质数的倍数为非质数
		}
	}
	return;
}

int main() {
	Initial();
	int n;
	while (scanf("%d", &n) != EOF) {
		bool isOutput = false;           //判断是否有输出
		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");
	}
	system("pause");
	return EXIT_SUCCESS;
}
// 64 位输出请用 printf("%lld")