poj 2909 Goldbach's Conjecture （哥德巴赫猜想）

 1/*************************************************************************
 2	> File Name: code/poj/2909.cpp
 3	> Author: 111qqz
 4	> Email: rkz2013@126.com
 5	> Created Time: 2015年08月22日 星期六 14时25分34秒
 6 ************************************************************************/
 7
 8#include<iostream>
 9#include<iomanip>
10#include<cstdio>
11#include<algorithm>
12#include<cmath>
13#include<cstring>
14#include<string>
15#include<map>
16#include<set>
17#include<queue>
18#include<vector>
19#include<stack>
20#define y0 abc111qqz
21#define y1 hust111qqz
22#define yn hez111qqz
23#define j1 cute111qqz
24#define tm crazy111qqz
25#define lr dying111qqz
26using namespace std;
27#define REP(i, n) for (int i=0;i<int(n);++i)
28typedef long long LL;
29typedef unsigned long long ULL;
30const int inf = 0x3f3f3f3f;
31const int N=1<<16;
32bool not_prime[N];
33int prime[N];
34int prime_num;
35int n;
36
37void init(){
38    not_prime[0] = true;
39    not_prime[1] = true;
40    for ( int i  =2 ; i < N ; i++){
41	if (!not_prime[i]){
42	    prime[++prime_num] = i;
43	}
44	for ( int j = 1  ; j <= prime_num&&i*prime[j]<N ; j++){
45	    not_prime[i*prime[j]] = true;
46	    if (i%prime[j]==0) break;
47	}
48    }
49}
50int main()
51{
52    init();
53    int n ;
54    while (scanf("%d",&n)&&n){
55	int ans = 0 ;
56	for ( int i = 2 ; i <= n /2 ; i++){
57	    if (!not_prime[i]&&!not_prime[n-i]){
58		ans++;
59	    }
60	}
61	printf("%d\n",ans);
62    }
63
64	return 0;
65}