hihocoder offer收割编程练习赛12 A 歌德巴赫猜想

思路：

枚举。

实现：

 #include <iostream>
 #include <cstdio>
 #include <algorithm>
 using namespace std;

 const int MAX_N = ;

 int prime[MAX_N];
 bool is_prime[MAX_N + ];

 int init(int n)
 {
     int p = ;
     for (int i = ; i <= n; i++)
         is_prime[i] = true;
     is_prime[] = is_prime[] = false;
     for (int i = ; i <= n; i++)
     {
         if (is_prime[i])
         {
             prime[p++] = i;
             for (int j =  * i; j <= n; j += i)
                 is_prime[j] = false;
         }
     }
     return p;
 }

 int main()
 {
     int num = init();
     int n;
     cin >> n;
     for (int i = ; i < num; i++)
     {
         if (binary_search(prime + i, prime + num, n - prime[i]))
         {
             int index = lower_bound(prime + i, prime + num, n - prime[i]) - prime;
             cout << prime[i] << " " << prime[index] << endl;
             break;
         }
     }
     return ;
 }