PAT甲级 1015. Reversible Primes (20)

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

判断一个数和他在D进制下的反转数是不是素数

#include<iostream>#include<cstdio>#include<cstring>#include<math.h>using namespace std;char s[10001];int cnt;void trans(int n,int d){    cnt=0;    while(n!=0)    {        s[cnt++]=n%d+'0';        n/=d;    }}int transback(int d){    int n=0;    for(int i=0;i<cnt;i++)    {        int g=s[i]-'0';        n=n*d+g;    }    return n;}bool isprime(int n){    if(n==0||n==1) return false;    for(int i=2;i*i<=n;i++)    {        if(n%i==0) return false;    }    return true;}int main(){    int n,d;    while(scanf("%d",&n)!=EOF&&n>=0)    {        scanf("%d",&d);        trans(n,d);        int k=0;        k=transback(d);        if(isprime(n)&&isprime(k))        cout<<"Yes"<<endl;        else cout<<"No"<<endl;    }    return 0;}