题解 | #素数回文#

//创建数组来求回文数，个人认为会更直观好理解
#include <stdio.h>
#include<string.h>
#include<math.h>
int Isprime(long long n) {
    for (int i = 2; i <= (long long)sqrt(n); i++) {
        if (n % i == 0) {
            return 0;
            break;
        }
    }
    return 1;
}
int main() {
    char arr[20] = { 0 };
    scanf("%s", arr);
    int num = strlen(arr) ;
    long long n = 0, m = 1;
    for (int i = num, k = 2; i < 2 * num - 1; i++, k += 2) {
        arr[i] = arr[i - k];
    }
    for (int k = num * 2 - 2; k >= 0; k--) { //求回文数
        n += (arr[k] - 48) * m;
        m *= 10;
    }
    if (Isprime(n))
        printf("prime\n");
    else
        printf("noprime\n");
    return 0;
}