Submission #583502

#	Time	Username	Problem	Language	Result	Execution time	Memory
583502		WongChun1234	The Xana coup (BOI21_xanadu)	C++14	100 / 100	146 ms	27484 KiB

xanadu

#include<bits/stdc++.h>
using namespace std;
const int N=100050;
int n,u,v;
long long dp[2][2][N];
bool st[N];
vector<int> adj[N];
void dfs(int nde,int par=-1){
	//flip now? is on?
	bool pt=1;
	long long curr[2][2][2]={{{0,0},{0,0}},{{INT_MAX,INT_MAX},{INT_MAX,INT_MAX}}};
	//chosen%2 flip this
	for (int i:adj[nde]){
		if (i==par) continue;
		dfs(i,nde);
		curr[0][0][pt]=min(curr[0][0][!pt]+dp[0][0][i],curr[1][0][!pt]+dp[1][0][i]);
		curr[0][1][pt]=min(curr[0][1][!pt]+dp[0][1][i],curr[1][1][!pt]+dp[1][1][i]);
		curr[1][0][pt]=min(curr[1][0][!pt]+dp[0][0][i],curr[0][0][!pt]+dp[1][0][i]);
		curr[1][1][pt]=min(curr[1][1][!pt]+dp[0][1][i],curr[0][1][!pt]+dp[1][1][i]);
		//cerr<<nde<<"::"<<curr[0][0][pt]<<" "<<curr[0][1][pt]<<" "<<curr[1][0][pt]<<" "<<curr[1][1][pt]<<"\n";
		pt^=1;
	}
	//no flip
	dp[0][0][nde]=curr[st[nde]][0][!pt];
	dp[0][1][nde]=curr[!st[nde]][0][!pt];
	//flip
	dp[1][0][nde]=curr[!st[nde]][1][!pt]+1;
	dp[1][1][nde]=curr[st[nde]][1][!pt]+1;
	//cout<<nde<<"::"<<st[nde]<<": noflip:"<<dp[0][0][nde]<<" "<<dp[0][1][nde]<<" flip:"<<dp[1][0][nde]<<" "<<dp[1][1][nde]<<"\n";
}
int main(){
	cin>>n;
	for (int i=1;i<n;i++){
		cin>>u>>v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	for (int i=1;i<=n;i++) cin>>st[i];
	dfs(1);
	long long ans=min(dp[0][0][1],dp[1][0][1]);
	if (ans>=1e9) cout<<"impossible\n";
	else cout<<ans<<"\n";
}

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