caioj.1036 搜索初步

统计出栈

//CATALAN数

#include<bits/stdc++.h>using namespace std;template <typename T> void read(T &x){x=0;int f=1;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-1;for(;isdigit(ch);ch=getchar())x=(x<<1)+(x<<3)+ch-'0';x*=f;}int n;int ans;void dfs(int a,int b,int c){if(c==n) {ans++;return;}if(a>0&&b<n) dfs(a-1,b+1,c);if(b>0&&c<n) dfs(a,b-1,c+1);}int main(){read(n);dfs(n,0,0);cout<<ans<<endl; return 0;}