```
#include <bits/stdc++.h>
using namespace std;
int a[20][20];
int main()
{
int n;
cin>>n;
for (int y=0;y<=n;y++) a[0][y]=1;
for (int x=1;x<=n;x++)
{
for (int y=x;y<=n;y++)
{
if (x==y) a[x][y]=a[x-1][y];
else a[x][y]=a[x-1][y]+a[x][y-1];
}
}
cout<<a[n][n];
return 0;
}
```
by yeyixiao2012 @ 2023-11-22 20:34:00
栓q
by haizaoatoutou @ 2023-11-27 15:39:31