找规律， f[n]跟f[n-1]和f[n-2]明显有关。。。
#include #include #include #include #include #include #include #include #include #include #include using namespace std; #define FF(i, a, b) for(i=a; ib; i--) #define CLR(a, b) memset(a, b, sizeof(b)) #define CPY(a, b) memcpy(a, b, sizeof(a)) long long n; long long f[10000001]; int main() { f[1] = 0; f[2] = 3; f[3] = 6; int i; FF(i, 4, 10000001) { f[i] = f[i-1] * 2 + f[i-2] * 3; f[i] %= 1000000007; } while(cin>>n) cout< #include #include #include #include #include #include #include #include #include #include using namespace std; #define FF(i, a, b) for(i=a; ib; i--) #define CLR(a, b) memset(a, b, sizeof(b)) #define CPY(a, b) memcpy(a, b, sizeof(a)) long long n; long long f[10000001]; int main() { f[1] = 0; f[2] = 3; f[3] = 6; int i; FF(i, 4, 10000001) { f[i] = f[i-1] * 2 + f[i-2] * 3; f[i] %= 1000000007; } while(cin>>n) cout<