Submission #653250

#	Time	Username	Problem	Language	Result	Execution time	Memory
653250		inksamurai	The Xana coup (BOI21_xanadu)	C++17	100 / 100	141 ms	44760 KiB

xanadu

#include <bits/stdc++.h>
#define int ll
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define rng(i,c,n) for(int i=c;i<n;i++)
#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define vec(...) vector<__VA_ARGS__>
#define _3D2ZDxo ios::sync_with_stdio(0),cin.tie(0)
typedef long long ll;
using pii=pair<int,int>;
using vi=vector<int>;
void print(){cout<<'\n';}
template<class h,class...t>
void print(const h&v,const t&...u){cout<<v<<' ',print(u...);}

void chmin(int&a,int b){
	a=min(a,b);
}

signed main(){
_3D2ZDxo;
	int n;
	cin>>n;
	vec(vi) adj(n);
	rep(i,n-1){
		int u,v;
		cin>>u>>v;
		u-=1,v-=1;
		adj[u].pb(v);
		adj[v].pb(u);
	}
	vi a(n);
	rep(i,n){
		cin>>a[i];
	}
	rep(i,n){
		a[i]^=1;
	}
	const int inf=1e9;
	vec(vec(vi)) dp(n,vec(vi)(2,vi(2,inf)));
	auto dfs=[&](auto self,int v,int par)->void{
		for(auto u:adj[v]){
			if(u==par) continue;
			self(self,u,v);
		}
		vi fdp(2); // flip the root
		fdp[a[v]^1]=1;
		fdp[a[v]]=inf;
		for(auto u:adj[v]){
			if(u==par) continue;
			vi nfdp(2,inf);
			{
				int t=0;
				rep(t1,2){
					rep(wit,2){
						int nwit=wit^t1;
						chmin(nfdp[nwit],fdp[wit]+dp[u][t][t1]);
					}
				}
			}
			fdp=nfdp;
		}
		vi gdp(2); 
		gdp[a[v]]=0;
		gdp[a[v]^1]=inf;
		for(auto u:adj[v]){
			if(u==par) continue;
			vi ngdp(2,inf);
			{
				int t=1;
				rep(t1,2){
					rep(wit,2){
						int nwit=wit^t1;
						chmin(ngdp[nwit],gdp[wit]+dp[u][t][t1]);
					}
				}
			}
			gdp=ngdp;
		}
		rep(t,2){
			chmin(dp[v][t][1],fdp[t]);
			chmin(dp[v][t][0],gdp[t]);
		}
	};
	dfs(dfs,0,-1);
	int ans=min(dp[0][1][0],dp[0][1][1]);
	if(ans>=inf){
		print("impossible");
	}else{
		print(ans);
	}
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30