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：

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;


#define MAX_N 64
#define MAX_M 1000000

int T, N;
int cnt[MAX_N];
int p[MAX_M];

int is_prime(int n) {
    for (int i = 2; i * i <= n; i++)
        if (n % i == 0)
            return 0;
    return 1;
}

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    p[1] = 0;
    for (int i = 2; i < MAX_M; i++)
        p[i] = p[i - 1] + is_prime(i);
    cin >> T;
    while (T--) {
        cin >> N;
        memset(cnt, 0, sizeof(cnt));
        cnt[0] = 1;
        for (int i = 1; i <= N; i++)
            cnt[i] = cnt[i - 1] + (i - 4 >= 0 ? cnt[i - 4] : 0);
        cout << p[cnt[N]] << endl;
    }
    return 0;
}