POJ 1595 素数打表水题

// 224K 16Ms
#include<iostream>
using namespace std;
#define N 2000
bool isprime
;
int prime
,nprime;

void doprime(int n)
{
int i,j;
nprime = 1;
memset(isprime,true,sizeof(isprime));
isprime[1] = 0;
prime[0] = 1;
for(i = 2;i<=n;i++)
{
if(isprime[i])
{
prime[nprime++] = i;
for(j = i*i;j<=n;j+=i)
{
isprime[j] = false;
}
}
}
}

int main()
{
int n,c;
while(cin>>n>>c)
{
doprime(n);
//acout<<nprime<<endl;
if(nprime<2*c)
{
cout<<n<<" "<<c<<": ";
for(int i = 0;i<nprime;i++)
cout<<prime[i]<<" ";
cout<<endl<<endl;
}
else
{
if(nprime%2==0)//擦！！！！！
{
cout<<n<<" "<<c<<": ";
for(int i = (nprime-2*c)/2;i<(nprime + 2*c)/2;i++)
cout<<prime[i]<<" ";
cout<<endl<<endl;
}
else
{
cout<<n<<" "<<c<<": ";
for(int i = (nprime-(2*c-1))/2;i< (nprime + (2*c-1))/2;i++)
cout<<prime[i]<<" ";
cout<<endl<<endl;
}
}

}
return 0;
}