点击链接PAT甲级-AC全解汇总
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 (<10?5?? ) 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
-2
Sample Output:
Yes
Yes
No
题意：
一行输入两个数字ab，判断a本身是不是素数，a经过b进制转换后逆序再转换回来后，是不是素数，如果都是素数则输出yes，否则no
我的代码：
#include<bits/stdc++.h>
using namespace std;bool is_prime(int num)
{
if(num==0||num==1)return false;for(int i=2;i<=sqrt(num);i++)if(num%i==0)return false;return true;
}
int main()
{
int num,radix;cin>>num;while(num>=0){
cin>>radix;if(!is_prime(num))cout<<"No"<<endl;else{
//转成radix进制,同时逆序string str;while(num){
str+=num%radix+'0';num/=radix;}//转成intint ans=0;for(int i=0;i<str.length();i++){
ans=ans*radix+(str[i]-'0');}//判断素数if(is_prime(ans))cout<<"Yes"<<endl;else cout<<"No"<<endl;}cin>>num;}return 0;
}