PAT1015. Reversible Primes

//题的理解是n在基数b中的的表示中,正序和逆序值都是素数,但是其实可直接判断n,因为n在b中的正常序列值就是再换成十进制就是n,但是不A;不知道为什么

用笨方法,先把n展开成b进制,正常计算其实是翻转值,倒序是正常序列值,两者都是素数时,yes,否则no,A了

也可以用atoi或者itoa但是本地可以,linix系统不支持这两个c函数,可以用c++里的string试试,直接把字符串变成数值貌似可以,小白还没解锁该技巧;

#include<cstdio>
#include<cmath>
int isprim(int s)
{
int i,t=(int)sqrt(s);
if(s<=1)return 0;
for(i=2;i<=t;i++)
if(s%i==0)return 0;
return 1;
}
int main()
{
freopen("input.txt","r",stdin);
int i,n,b;
while(scanf("%d",&n)!=EOF&&n>=0)
{
//if(!isprim(n))printf("No\n");
//else
{
scanf("%d",&b);
int len=0,s[33];
do
{
s[len++]=n%b;
n=n/b;
}while(n!=0);
int s1=0,s2=0;
for(i=len-1;i>=0;i--)s1=s1*b+s[i];
for(i=0;i<len;i++)s2=s2*b+s[i];
//printf("%d\n",n);
if(isprim(s1)&&isprim(s2)) printf("Yes\n");
else printf("No\n");
}
}
return 0;
}

时间: 2024-08-11 05:45:37

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