H_n = \binom{2n}{n} - \binom{2n}{n-1}
$$
-```
-f[n] = f[0] * f[n - 1] + f[1] * f[n - 2] + ... + f[n - 1] * f[0]
-```
+ f[n] = f[0] * f[n - 1] + f[1] * f[n - 2] + ... + f[n - 1] * f[0]
-具体实例
-[https://www.luogu.org/problem/P1044](洛谷 P1044 栈)
-```
+具体实例[https://www.luogu.org/problem/P1044](洛谷 P1044 栈)
-#include <iostream>
+ #include <iostream>
-using namespace std;
+ using namespace std;
-int n;
-long long f[25];
-
-int main(){
- f[0] = 1;
- cin >> n;
- for(int i = 1; i <= n; i++)
- f[i] = f[i - 1] * (4 * i - 2) / (i + 1);
- //这里用的是常见公式2
- cout << f[n] << endl;
- return 0;
-}
-```
+ int n;
+ long long f[25];
+ int main(){
+ f[0] = 1;
+ cin >> n;
+ for(int i = 1; i <= n; i++)
+ f[i] = f[i - 1] * (4 * i - 2) / (i + 1);
+ //这里用的是常见公式2
+ cout << f[n] << endl;
+ return 0;
+ }
## 路径计数问题