hdu 1397 (素数判定)

一开始提交了这个，果断TLE

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <string>
 4 #include <queue>
 5 #include <vector>
 6 #include <map>
 7 #include <cmath>
 8 using namespace std;
 9
10 #define MEM(a,v) memset (a,v,sizeof(a))
11 // a for address, v for value
12
13 #define max(x,y) ((x)>(y)?(x):(y))
14 #define max(x,y) ((x)>(y)?(x):(y))
15
16 #define debug printf("!\n")
17
18
19 bool isPrime(int n)
20 {
21           int i;
22           for(i = 3;i<=sqrtf(n);i++)
23           {
24                     if(n%i == 0)
25                               return false;
26           }
27           return true;
28 }
29
30
31 int main()
32 {
33           int n;
34           int i,j;
35           int count;
36           while(scanf("%d",&n)!=EOF && n)
37           {
38                     count = 0;
39                     for(i = 3;i<=n/2;i+=2)
40                     {
41                               if(isPrime(i))
42                                         if(isPrime(n-i))
43                                                   count++;
44                     }
45                     printf("%d\n",count);
46           }
47
48           return 0;
49 }

看来只能打表了

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <string>
 4 #include <queue>
 5 #include <vector>
 6 #include <map>
 7 #include <cmath>
 8 using namespace std;
 9
10 #define MEM(a,v) memset (a,v,sizeof(a))
11 // a for address, v for value
12
13 #define max(x,y) ((x)>(y)?(x):(y))
14 #define max(x,y) ((x)>(y)?(x):(y))
15
16 #define debug printf("!\n")
17
18 const int MM = 32769;
19
20 bool isPrime[MM] = {false};
21
22 void initPrime()
23 {
24           MEM(isPrime,true);
25           int i,j;
26
27           for(i = 1;i<=MM-1;i++) if(i%2==0) isPrime[i]=false;
28           for(i = 3;i<=MM/2+1;i++)
29           {
30                     for(j = i+i;j<=MM-1;j+=i)
31                               isPrime[j] = false;
32           }
33           isPrime[1] = false;
34           isPrime[2] = true;
35 }
36
37
38 int main()
39 {
40
41           int i,n;
42           initPrime();
43           while(scanf("%d",&n)!=EOF && n)
44           {
45                     int count = 0;
46                     for(i = 2;i<=n/2;i++)
47                               if(isPrime[i] && isPrime[n-i])
48                                         count++;
49                     printf("%d\n",count);
50           }
51
52           return 0;
53 }

421MS