29 pts 求条

#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,S;
int a[10000],ans[10000];
void dfs1(int l,int sum)
{
	if(l>n/2)
	{
		ans[sum]++;
		return ;
	}
	dfs1(l+1,sum);
	dfs1(l+1,sum+a[l]);
}
int dfs2(int l,int sum)
{
	if(l>n) return ans[S/2-sum];
	return dfs2(l+1,sum)+dfs2(l+1,sum+a[l]);
}
signed main()
{
	cin>>n;
	S=n*(n+1)/2; 
	if(S%2)
	{
		cout<<0;
		return 0;
	}
	for(int i=1;i<=n;i++) a[i]=i;
	dfs1(1,0);
	cout<<dfs2(n/2+1,0)/2;
	return 0;
}