PAT甲级1015

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:

YesYesNo

#include<cstdio>#include<vector>#include<algorithm>using namespace std;bool isPrime(int a){if (a < 2)return false;for (int i = 2; i <= sqrt(a); i++){if (a % i == 0){return false;}}return true;}bool reversePrime(int a, int radix){if (isPrime(a)){vector<int> v;do{v.push_back(a%radix);a /= radix;} while (a);int sum = 0;for (int i = 0; i < v.size(); i++){sum += v[i] * pow(radix, v.size()-1-i);}if (isPrime(sum))return true;elsereturn false;}elsereturn false;}int main(){int N, radix;while (1){scanf("%d", &N);if (N < 0)break;scanf("%d", &radix);if (reversePrime(N, radix)){printf("Yes\n");}elseprintf("No\n");}return 0;}