Submission #526028

#	Time	Username	Problem	Language	Result	Execution time	Memory
526028		Gurban	The Xana coup (BOI21_xanadu)	C++17	30 / 100	46 ms	15480 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;

using ll = long long;

const int maxn=1e5+5;
int n;
int col[maxn];	
ll dp[maxn][2][2];
vector<int>E[maxn];

void dfs(int nd,int pr){
	if((int)E[nd].size() == 1 and E[nd][0] == pr){
		if(!col[nd]){
			dp[nd][0][0] = 0;
			dp[nd][0][1] = 1e9;
			dp[nd][1][0] = 1e9;
			dp[nd][1][1] = 1;
		}
		else {
			dp[nd][1][0] = 0;
			dp[nd][1][1] = 1e9;
			dp[nd][0][0] = 1e9;
			dp[nd][0][1] = 1;
		}
		return;
	}
	for(auto i : E[nd]) if(i != pr) dfs(i,nd);

	if(!col[nd]){
		int bef[2]; bef[0] = 0,bef[1] = 1e9;
		for(auto i : E[nd]) if(i != pr){
			int now[2];
			now[0] = min(bef[0] + dp[i][0][0],bef[1] + dp[i][0][1]);
			now[1] = min(bef[0] + dp[i][0][1],bef[1] + dp[i][0][0]);
			
			bef[0] = now[0];
			bef[1] = now[1];
		}
		dp[nd][0][0] = bef[0];
		dp[nd][1][0] = bef[1];

		bef[0] = 0,bef[1] = 1e9;
		for(auto i : E[nd]) if(i != pr){
			int now[2];
			now[0] = min(bef[0] + dp[i][1][0],bef[1] + dp[i][1][1]);
			now[1] = min(bef[0] + dp[i][1][1],bef[1] + dp[i][1][0]);
			
			bef[0] = now[0];
			bef[1] = now[1];
		}
		dp[nd][0][1] = bef[1] + 1;
		dp[nd][1][1] = bef[0] + 1;
	}
	else {
		int bef[2]; bef[0] = 0,bef[1] = 1e9;
		for(auto i : E[nd]) if(i != pr){
			int now[2];
			now[0] = min(bef[0] + dp[i][0][0],bef[1] + dp[i][0][1]);
			now[1] = min(bef[0] + dp[i][0][1],bef[1] + dp[i][0][0]);
			
			bef[0] = now[0];
			bef[1] = now[1];
		}
		dp[nd][0][0] = bef[1];
		dp[nd][1][0] = bef[0];

		bef[0] = 0,bef[1] = 1e9;
		for(auto i : E[nd]) if(i != pr){
			int now[2];
			now[0] = min(bef[0] + dp[i][1][0],bef[1] + dp[i][1][1]);
			now[1] = min(bef[0] + dp[i][1][1],bef[1] + dp[i][1][0]);
			
			bef[0] = now[0];
			bef[1] = now[1];
		}
		dp[nd][0][1] = bef[0] + 1;
		dp[nd][1][1] = bef[1] + 1;
	}
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n;
	for(int i = 1;i <= n;i++) for(int j = 0;j < 2;j++) for(int k = 0;k < 2;k++) dp[i][j][k] = 1e9;
	for(int i = 1;i < n;i++){
		int x,y; cin >> x >> y;
		E[x].push_back(y);
		E[y].push_back(x);
	}
	for(int i = 1;i <= n;i++) cin >> col[i];
	dfs(1,0);
	// for(int i = 1;i <= n;i++){
	// 	cout<<i<<' ';
	// 	for(int j = 0;j < 2;j++) for(int k = 0;k < 2;k++) cout<<dp[i][j][k]<<' ';
	// 	cout<<'\n';
	// }
	int ans = min(dp[1][0][0],dp[1][0][1]);
	if(ans >= 1e9) cout<<"impossible";
	else cout<<ans;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 0 / 40
• Subtask 5: 0 / 30