UVa 543 - Goldbach's Conjecture

　　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+> bs;

 void sieve(ll upper)
 {
     bs.set();
     bs.set(, false);
     bs.set(, false);
     for (ll i = ; 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 = ;
         bool ok = false;
         while (primes[idx] *  <= n)
         {
             int t = n - primes[idx];
             if (bs.test((size_t)t))
             {
                 ok = true;
                 break;
             }
             idx++;
         }
         if (ok)  printf("%d = %d + %d\n", n, primes[idx], n-primes[idx]);
         else  printf("Goldbach's conjecture is wrong.\n");
     }
     return ;
 }