素数问题

http://poj.org/problem?id=2689

筛选素数 先建一个小素数表 2-sqrt（max) 再根据这个表来进行区间素数的筛选

View Code

 1 #include<math.h>

 2 #include<stdio.h>

 3 #include<string.h>

 4 __int64 x[1000011];

 5 int pr[46500],pd[46500],pg[1000011];

 6 int main()

 7 {

 8     __int64  n,m,x1,x2,x3,x4,y;

 9     int i,j,k;

10     for(i = 2 ; i <= 46500 ; i++)

11     {

12         if(!pr[i])

13         {

14             for(j = i+i ; j <= 46500 ; j+=i)

15             if(pr[j])

16             pr[j] = 1;

17         }

18     }

19     int g = 0;

20     for(i = 2 ; i <= 46500 ; i++)

21     if(!pr[i])

22     pd[g++] = i;

23     while(scanf("%I64d%I64d",&n,&m)!=EOF)

24     {

25         memset(pg,0,sizeof(pg));

26         k = 0;

27         for(i = 0 ;i < g ; i++)

28         {

29             if(n%pd[i])

30             y = n/pd[i]+1;

31             else

32             y = n/pd[i];

33             if(n<=pd[i])

34             y++;

35             for(j = y*pd[i]-n ; j <= m-n ; j+=pd[i])

36             if(!pg[j])

37                 pg[j] = 1;

38         }

39         if(n==1)

40             pg[0] = 1;

41         k = 0;

42         for(i = 0 ; i <= m-n ; i++)

43         if(!pg[i])

44         {

45             x[k++] = i+n;

46         }

47         if(k>1)

48         {

49             __int64 min = x[1]-x[0],max=0;

50             x3 = x[0];

51             x4 = x[1];

52             for(i = 1 ;i <k ; i++)

53             {

54                 if(x[i]-x[i-1]>max)

55                 {

56                     max = x[i]-x[i-1];

57                     x2 = x[i];

58                     x1 = x[i-1];

59                 }

60                 if(x[i]-x[i-1]<min)

61                 {

62                     min = x[i]-x[i-1];

63                     x4 = x[i];

64                     x3 = x[i-1];

65                 }

66             }

67             printf("%I64d,%I64d are closest, %I64d,%I64d are most distant.\n",x3,x4,x1,x2);

68         }

69         else

70         printf("There are no adjacent primes.\n");

71     }

72     return 0;

73 }