PAT A1015. Reversible Primes

1015. Reversible Primes (20)

时间限制

400 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (< 10⁵) and D (1 < D <= 10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:

The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:

For each test case, print in one line "Yes" if N is a reversible prime with radix D, or "No" if not.

Sample Input:

73 1023 223 10-2

Sample Output:

YesYes
No
#include <stdio.h>#include <math.h>int prime(int num) {int sqr, flag, i;if(num == 1) {return 0;}sqr = (int) sqrt(num);flag = 1;for(i = 2; i <= sqr; i ++) {if(num % i == 0) {flag = 0;break;}}return flag;}int main() {int num[20] = {-1};int N, D, i, j, reverseN;while(scanf("%d", &N) && N > 0) {scanf("%d", &D);if(prime(N) != 1) {printf("No\n");continue;}i = 0;while(N != 0) {num[i ++] = N % D;N /= D;}for(j = 0, reverseN = 0; j < i; j ++) {reverseN = D * reverseN + num[j];}//printf("reverseN: %d\n", reverseN);if(prime(reverseN) == 1) {printf("Yes\n");} else {printf("No\n");}}return 0;}