題目鏈接：https://www.luogu.org/problemnew/show/P1865

其實就是埃拉托色尼篩素數模板...

好像每個數暴力枚舉到sqrt()也可以...就算當我無聊練手罷

 1 #include <cstdio>
 2 #include <cmath>
 3 #include <algorithm>
 4 #include <cstring>
 5 using namespace std;
 6 const int maxn = 1000000 + 10;
 7 bool prime[maxn];
 8 int n, m, left, right, sq, tot = 0
 
;
 9 int main()
10 {
11     memset(prime,0,sizeof(prime));
12     scanf("%d%d", &n, &m);
13     
14     sq = sqrt(m);
15     prime[1] = 1;
16     for(int i = 2; i <= sq; i++)
17         if(prime[i] == 0)
18         {
19             for(int j = i*i; j <= m; j+=i)
20             prime[j] = 1
 
;
21         }
22     
23     for(int i = 1; i <= n; i++)
24     {
25         scanf("%d%d", &left, &right);
26         if(left > m || right > m || left <= 0 || right <= 0) 
27         {
28             printf("Crossing the line\n");
29             continue;
30         }
31         else
 

32         {
33             for(int j = left; j <= right; j++)
34             {
35                 if(prime[j] == 0)
36                 tot++;
37             }    
38             printf("%d\n",tot);
39             tot = 0;
40         }
41     
42     }
43     return 0;
44 }

【luogu P1865 A % B Problem】題解