poj Prime Gap

 1 #include<iostream>

 2 #include<cstdio>

 3 #include<cstdlib>

 4 #include<cstring>

 5 #include<string>

 6 #include<queue>

 7 #include<algorithm>

 8 #include<map>

 9 #include<iomanip>

10 #include<climits>

11 #include<string.h>

12 #include<numeric>

13 #include<cmath>

14 #include<stdlib.h>

15 #include<vector>

16 #include<stack>

17 #include<set>

18 #define INF 1e7

19 #define MAXN 100010

20 #define maxn 1000010

21 #define Mod 1000007

22 #define N 1299800

23 using namespace std;

24 typedef long long LL;

25 

26 int prime[N];

27 int vis[N];

28 void run()

29 {

30     int k = 1;

31     for (LL i = 2; i <= N; ++i)

32         if (!vis[i]) {

33             prime[k++] = i;

34             for (LL j = i*i; j < N; j += i)

35                 vis[j] = 1;

36         }

37     /*for (int i = 1; i < 1300; ++i)

38         cout << prime[i] << " ";

39     cout << endl;*/

40 }

41 

42 int n;

43 int ans = 0;

44 

45 int main()

46 {

47     run();

48     while (cin >> n,n) {

49         ans = 2;

50         if (vis[n] == 0)

51             ans = 0;

52         else {

53             int tmp = n;

54             while (--tmp) 

55                 if (vis[tmp]) 

56                     ans++;

57                 else break;

58             tmp = n;

59             while (++tmp)

60                 if (vis[tmp])

61                     ans++;

62                 else break;

63         }

64         cout << ans << endl;

65     }

66     return 0;

67 }