题解 | #素数回文#

#include <stdio.h>

int is_suShu(long long int a) {//判断是否时素数
    int res = 1;
    if (a == 1) return 0; //1不是素数，直接返回
    // for (long long int i = 2; i < a; i++) {
    //判断i的平方即可，不用到i<a,否则因为数字太大而超时，参考题解或https://blog.csdn.net/huang_miao_xin/article/details/51331710
    for (long long int i = 2; i * i <= a; i++) {
        if (a % i == 0) return 0;
    }
    return res;
}

long long int huiWenShu(int n) {//把输入的数字变成回文数
    long long int res = n;
    int yuShu;//余数
    int a[10];
    int index = 0;
    while (n != 0)
    {
        yuShu = n % 10;
        a[index] = yuShu;
        index++;
        n = n / 10;
    }

    for (int i = 1; i < index; i++) {
        res = res * 10 + a[i];
    }
    return res;
}

int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        long long int res = huiWenShu(n);
        if (is_suShu(res) == 1) printf("prime\n");
        else printf("noprime\n");
    }
    return 0;
}