1015. Reversible Primes (20)
题目链接：http://www.patest.cn/contests/pat-a-practise/1015
题目：
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 10 23 2 23 10 -2Sample Output:
Yes Yes No
分析：
判断是否是质数，以及加上数制转换。
这里的是指原数字与它在数制下的倒叙，如23 2，是10111（2）的倒叙11101的真实数字。判断原数与倒叙数字是否都是质数判别。
案例分析：
73 10，73是质数，10进制下的倒叙数是37，也是质数，Yes
23 2， 23是质数，2进制下表示为10111，倒叙数是11101，转换为10进制为29，也是质数，Yes
23 10，23是质数，10进制下的倒叙数是32，不是质数，No
AC代码：
#include<stdio.h>
using namespace std;
bool isPrime(int num1){//判断是否是质数
if(num1 < 2) return false;
if(num1 == 2 || num1 == 3)return true;
for(int i = 2; i * i <= num1; i ++){
if(num1 % i == 0)return false;
}
return true;
}
int rev_num(int num1,int radix){//判断基数radix下的倒叙数（还是转换为10进制的）
int num2 = 0;
while(num1){
num2 *= radix;
num2 += num1 % radix;
num1 /= radix;
}
return num2;
}
int main(void){
int n,d;
while(scanf("%d",&n) != EOF){
if(n < 0) break;//输出是以复数作为结束的
scanf("%d",&d);
int n_rev;
n_rev = rev_num(n,d);
if(isPrime(n) == true && isPrime(n_rev) == true) //如果原数和倒叙数都是质数
puts("Yes");
else
puts("No");
}
return 0;
}
——Apie陈小旭
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 10 23 2 23 10 -2Sample Output:
Yes Yes No