codeup【递归入门】出栈序列统计_codeup编程_战斗的咸鱼的博客-CSDN博客

#include<iostream>
using namespace std;
int n,sum,ans;
void dfs(int out,int in,int not_in){
	if(out==n){
		ans++;
		return;
	}
	if(in>0) dfs(out+1,in-1,not_in);
	if(not_in>0&&in<n) dfs(out,in+1,not_in-1);
}
int main(){
	cin>>n;
	dfs(0,0,n);
	cout<<ans<<endl;
	return 0;
}