Odd-Even Subsequence T17 D57

Problem - D - Codeforces (Unofficial mirror site, accelerated for Chinese users)

思路

交互题

将每条边按dfs序保存起来。

每次询问一半的边，若询问的值不等于最大值，递归另一半。

参考代码

#include<bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
#define fi first
#define se second
#define pb push_back
#define si size()
#define ls (p<<1)
#define rs ((p<<1)|1)
#define mid (t[p].l+t[p].r)/2 
using namespace std;
ll read(){ll x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}return x*f;}
inline void Prin(ll x){if(x < 0){putchar('-');x = -x;}if(x > 9) Prin(x / 10);putchar(x % 10 + '0');}
 
const int inf=0x3f3f3f3f;
const ll mod=1000000007;
const int qs=2e3+7;
 
int T,n,k,a[qs],cnt=0; 
int u[qs];
vector< int > v[qs];
vector< pii > ans;
void dfs(int x,int fa){
	
	for(int i=0;i<v[x].si;++i){
		int p=v[x][i];
		if(p==fa) continue;
		ans.pb({x,p});
		dfs(p,x);
	}
}
int Max=0;
void solve(int l,int r){
	if(l==r){
		cout<<"! "<<ans[l].fi<<" "<<ans[l].se<<"\n";
		cout.flush();
		return;
	}
	int md=(l+r)/2;
	int cnt=0;
	cout<<"?";
	
	for(int i=l;i<=md;++i){
		a[++cnt]=ans[i].fi,a[++cnt]=ans[i].se;
	} 
	sort(a+1,a+1+cnt);
	cnt=unique(a+1,a+1+cnt)-a-1;
	cout<<" "<<cnt;
	for(int i=1;i<=cnt;++i) cout<<" "<<a[i];
	cout<<"\n";
	cout.flush();
	int ft;
	cin>>ft;
	if(ft==Max){
		Max=ft;
		solve(l,md);	
	}
	else{
		solve(md+1,r);
	}
}
 
int main(){
	cin>>n;
	int x,y;
	for(int i=1;i<n;++i){
		cin>>x>>y;
		v[x].pb(y);
		v[y].pb(x);
	}
	dfs(1,0);
	cout<<"?";
	cout<<" "<<n;
	for(int i=1;i<=n;++i) cout<<" "<<i;
	cout<<"\n";
    cout.flush();
    cin>>Max;
	solve(0,ans.size()-1);
	
	return 0;
}