HDU1262

打素数表

#include<stdio.h>
#include<string.h>
const int maxn = 10010;
int shu[ maxn ],prime[ maxn ];
void get_prime( ){
    for( int i=1;i<maxn;i+=2 ) shu[ i ]=1;
    for( int i=0;i<maxn;i+=2 ) shu[ i ]=0;//0 is stand for not prime
    shu[ 1 ]=0;
    shu[ 2 ]=1;
    for( int i=3;i<maxn;i+=2 ){
        if( shu[i]==1 ){
            int t,delta;
            delta=i*2;
            t=delta+i;
            while( t<maxn ){
                shu[ t ]=0;
                t+=delta;
            }
        }
    }
    /*
    prime[1]=2;
    int cnt=2;
    for( int i=3;i<maxn;i++ ){
        if( shu[i]==1 ){
            prime[ cnt++ ]=i;
        }
    }
    */
}
int main(){
    int m;
    get_prime();
    while( scanf("%d",&m)==1 ){
        for( int i=m/2;;i-- ){
            if( shu[i]==1&&shu[m-i]==1 ){
                printf("%d %d\n",i>(m-i)?(m-i):i,i>(m-i)?i:(m-i));
                break;
            }
        }
    }
    return 0;
}