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
#include<bits/stdc++.h>
using namespace std;
const int N = 100000+5;
int p[N], prim[N], c, d[111], dl;
void findPrim(int n){
for(int i = 2; i <= n; i++)
if(p[i]==0){
prim[c++]=i;
for(int j = i+i; j <= n; j+=i)p[j]=1;
}
}
int reverRadix(int n, int r){
dl=0;
while(n){
d[dl++] = n%r;
n /= r;
}
for(int i = 0; i < dl; i++)
n = n*r + d[i];
return n;
}
int main(){
findPrim(N);
p[1] = 1; //测试点1报错
while(1){
int n, d;
scanf("%d", &n);
if(n < 0) return 0;
scanf("%d", &d);
if(p[n]) printf("No\n");
else if(p[reverRadix(n, d)]) printf("No\n");
else printf("Yes\n");
}
return 0;
}
总结
1、 #数学问题
测试点1报错，原因是1不是素数也不是合数，需要添加特判p[1] = 1;