#include <cstdio>
#include <cstring>
const int N = 50000;
bool a[N];
int p[N];
int n=50000;
void Prime2() 
{
	memset(a, 0, n*sizeof(a[0]));
	int num = 0, i, j;
	for(i = 2; i < n; ++i) 
	{
		if(!(a[i])) p[num++] = i;
		for(j = 0; (j<num && i*p[j]<n); ++j) 
		{
			a[i*p[j]] = 1;
			if(!(i%p[j])) break;
		}
	}
}
int main()
{
	int number;
	Prime2();
	a[0]=true,a[1]=true;
	while(scanf("%d",&number)!=EOF && number)
	{
		int ans=0;
		for(int i=0;p[i]<number/2+1;++i)if(!a[number-p[i]])++ans;
		printf("%d\n",ans);
	}
	return 0;
}

• 0ms做法 (514) 20121181jj 2014-02-14 21:34:22