1015. 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:

YesYesNo

题目的意思是说：输入一个数n和d。判断n是不是素数，以及n在d进制下，用d进制表示n这个数的反转过来，再转化成十进制，看这个数是不是素数，如果都是素数则打印YES，否则打印No

#include<iostream>using namespace std;bool isPrime(int num);int reverseNumber(int num, int radix);int main(){int n, d;while(cin>>n){if(n < 0)break;cin>>d;int rev_n = reverseNumber(n, d);if(isPrime(n) && isPrime(rev_n))cout<<"Yes"<<endl;elsecout<<"No"<<endl;}return 0;}bool isPrime(int num){if(num < 2)return false;if(num ==2 || num == 3)return true;for(int i = 2; i*i <= num; i ++)if(num % i == 0)return false;return true;}int reverseNumber(int num, int radix){int rev_num = 0;while(num != 0){rev_num *= radix;rev_num += num % radix;num /= radix;}return rev_num;}