poj 2909 Goldbach's Conjecture

素数水题：

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<map>
#include<cstring>
#include<vector>
using namespace std;
int prime[10000],cnt=0;
bool hash[100024];
void Prime( )
{
    int t = ( int )sqrt( 100000.0 ) + 1;
    memset( hash , 0 ,sizeof( hash ) );
    for(int i = 3 ; i <= t ; i += 2 )  
    {
       if( !hash[i>>1] )
       {
          int x = i<<1;
          for( int j = i * i; j <= 100001 ; j += x )
          {
               hash[j>>1] = true;        
          }        
       }    
    }
    cnt = 0;
    prime[cnt++] = 2;
    t = 100000/2;
    for( int i = 1; i <=t ; i ++ )
    {
         if( !hash[i] )
         {
             prime[cnt++] =i * 2 + 1;    
         }
    }
    memset( hash , 0 ,sizeof( hash ) );
    for( int i = 0 ; i < cnt; i ++ )
    {
        hash[prime[i]] = true;
    }
}
int Solve( int num )
{ 
    int t =  num/2,sum=0;
    for( int i = 0 ;i < cnt ;i ++ )
    {
        if( prime[i] > t ) break;
        else
        {
            if( hash[num-prime[i]] )
            {
                sum ++;    
            }
        }    
    }     
    return sum;
}
int main(  )
{
    Prime();
    int num;
    while( scanf( "%d",&num ),num )
    {  
           printf( "%d\n",Solve( num ) );
    }
    //system( "pause" );
    return 0;
}