1007 

 1 #include<iostream>
 2 #include<vector>
 3 #include<cmath>
 4 
 5 using namespace std;
 6 
 7 int main()
 8 {
 9     vector<int> prim;
10     int n;
11     cin >> n;
12     for (int number = 2; number <= n; ++number)
13     {
14         int i = 2;
15         for (; i <= sqrt(number); ++i)
16             if (number % i == 0)
17                 break;
18         if (i > sqrt(number))
19             prim.push_back(number);
20     }
21     int cnt = 0;
22     for (int i = 0; i != prim.size() - 1; ++i)
23         if (prim[i + 1] - prim[i] == 2)
24             ++cnt;
25     cout << cnt;
26 
27     return 0;
28 }

注意穷举素数的算法

posted @ 2020-01-09 14:41  Huayra  阅读(399)  评论(0)  编辑  收藏  举报