题目信息
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
-2
Sample Output:
Yes
Yes
No
心得
又是刷PAT的一天，1014题还有一个测试点没通过。
只有一个感慨：论头发是怎么没的......
代码
#include<cstdio>
#include<cmath>
#include<vector>
bool isPrime(int n){
if(n<=1) return false;
int sqr=(int)sqrt(n*1.0);
for(int i=2;i<=sqr;i++){
if(n%i==0) return false;
}
return true;
}
using namespace std;
int main(){
int n=1,d;//n<100000&&d<=10
scanf("%d",&n);
while(n>=0){
scanf("%d",&d);
int before=n;
int ver=0;
vector<int> v;
while(n>0){
v.push_back(n%d);
n/=d;
}
for(int i=0;i<v.size();i++){
ver*=d;ver+=v[i];
}
if(isPrime(before)&&isPrime(ver)) printf("Yes\n");
else printf("No\n");
scanf("%d",&n);
}
return 0;
}
测试结果
image.png
