UVa 543

　　题目大意：给一个偶数，判断是否是两个素数的和。

　　先用sieve方法生成一个素数表，然后再进行判断即可。

#include <cstdio>
#include <vector>
#include <bitset>
using namespace std;
typedef vector<int> vi;
typedef long long ll;
#define MAXN 1000000

vi primes;
bitset<MAXN+100> bs;

void sieve(ll upper)
{
    bs.set();
    bs.set(0, false);
    bs.set(1, false);
    for (ll i = 2; i <= upper; i++)
        if (bs.test((size_t)i))
        {
            for (ll j = i*i; j <= upper; j += i)
                bs.set((size_t)j, false);
            primes.push_back((int)i);
        }
}

int main()
{
#ifdef LOCAL
    freopen("in", "r", stdin);
#endif
    sieve(MAXN);
    int n;
    while (scanf("%d", &n) && n)
    {
        int idx = 1;
        bool ok = false;
        while (primes[idx] * 2 <= n)
        {
            int t = n - primes[idx];
            if (bs.test((size_t)t))
            {
                ok = true;
                break;
            }
            idx++;
        }
        if (ok)  printf("%d = %d + %d
", n, primes[idx], n-primes[idx]);
        else  printf("Goldbach's conjecture is wrong.
");
    }
    return 0;
}