POJ 2262 Goldbach's Conjecture（Eratosthenes筛法）

#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
using namespace std;

const int maxn = 1e7 + 5;

int n;
int vis[maxn];

void init()
{
int m = sqrt(maxn + 0.5);
for (int i = 2; i < m; i++)
{
if (!vis[i])
for (int j = i*i; j < maxn; j += i)
vis[j] = 1;
}
}

int main()
{
//freopen("D:\\txt.txt", "r", stdin);
init();
while (cin >> n && n)
{
for (int i = 3; i < n; i++)
{
if (!vis[i])
{
if (!vis[n - i])
{
printf("%d = %d + %d\n", n, i, n - i);
break;
}
}
}
}
}