HackerRank# Red John is Back

原题地址

 

简单动归+素数判定，没用筛法也能过

 

代码：

 1 #include <cmath>

 2 #include <cstdio>

 3 #include <vector>

 4 #include <iostream>

 5 #include <algorithm>

 6 #include <cstring>

 7 using namespace std;

 8 

 9 

10 #define MAX_N 64

11 #define MAX_M 1000000

12 

13 int T, N;

14 int cnt[MAX_N];

15 int p[MAX_M];

16 

17 int is_prime(int n) {

18     for (int i = 2; i * i <= n; i++)

19         if (n % i == 0)

20             return 0;

21     return 1;

22 }

23 

24 int main() {

25     /* Enter your code here. Read input from STDIN. Print output to STDOUT */

26     p[1] = 0;

27     for (int i = 2; i < MAX_M; i++)

28         p[i] = p[i - 1] + is_prime(i);

29     cin >> T;

30     while (T--) {

31         cin >> N;

32         memset(cnt, 0, sizeof(cnt));

33         cnt[0] = 1;

34         for (int i = 1; i <= N; i++)

35             cnt[i] = cnt[i - 1] + (i - 4 >= 0 ? cnt[i - 4] : 0);

36         cout << p[cnt[N]] << endl;

37     }

38     return 0;

39 }