ABC 236 D（dfs

D - Dance

思路：
奇妙の搜索题
需要一些优化
code：

#include<bits/stdc++.h>
#define endl '\n'
#define ll long long
#define ull unsigned long long
#define ld long double
#define all(x) x.begin(), x.end()
#define eps 1e-6
using namespace std;
const int maxn = 30 + 9;
const int mod = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
ll n, m;

ll mp[maxn][maxn];
bool vis[maxn];
ll ans = 0;

void dfs(ll sum = 0){
	int i = 1;
	while(i <= 2 * n && vis[i]) ++i;
	if(i > 2 * n){
		ans = max(ans, sum);
		return;
	}
	for(int j = i + 1; j <= 2 * n; ++j) if(!vis[j])
	{
		vis[i] = vis[j] = 1;
		dfs(sum ^ mp[i][j]);
		vis[i] = vis[j] = 0;
	}
}
void work()
{
	cin >> n;
	for(int i = 1; i <= 2 * n - 1; ++i)
	{
		for(int j = i + 1; j <= 2 * n; ++j)
			cin >> mp[i][j];
	}	
	dfs(0);
	cout << ans;
}

int main()
{
	ios::sync_with_stdio(0);
//	int TT;cin>>TT;while(TT--)
	work();
	return 0;
}