Submission #677052

#	Time	Username	Problem	Language	Result	Execution time	Memory
677052		ajab_01	The Xana coup (BOI21_xanadu)	C++17	0 / 100	68 ms	17532 KiB

xanadu

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

#define int long long

const int N = 1e5 + 5;
const int INF = 1e9;
vector<int> g[N];
int dp[N][2][2] , sit[N] , root , n;

void dfs(int ver , int par){
	for(int i : g[ver]){
		if(i == par) continue;
		dfs(i , ver);
	}

	if((int)g[ver].size() == 1){
		dp[ver][sit[ver]][0] = 0;
		dp[ver][sit[ver] ^ 1][1] = 1;
		return;
	}

	for(int k = 0 ; k < 2 ; k++){
		int sum = 0 , summ = 0 , cnt = 0 , ch = 0;
		for(int i : g[ver]){
			if(i == par) continue;
			int mn = min(dp[i][k][0] , dp[i][k][1]);
			sum += mn;
			if(dp[i][k][0] == dp[i][k][1]) ch = 1;
			if(mn == dp[i][k][1]) cnt++;
		}

		summ = INF;
		for(int i : g[ver]){
			if(i == par) continue;
			summ = min(summ , sum - min(dp[i][k][0] , dp[i][k][1]) + max(dp[i][k][0] , dp[i][k][1]));
		}

		if(ch){
			dp[ver][0][k] = dp[ver][1][k] = sum;
			continue;
		}

		if(k == 1){
			dp[ver][sit[ver]][k] = (cnt & 1 ? sum : summ) + 1;
			dp[ver][sit[ver] ^ 1][k] = (cnt & 1 ? summ : sum) + 1;
		}
		else{
			dp[ver][sit[ver]][k] = (cnt & 1 ? summ : sum);
			dp[ver][sit[ver] ^ 1][k] = (cnt & 1 ? sum : summ);
		}
	}
}

int32_t main(){
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	cin >> n;
	for(int i = 0 ; i < n - 1 ; i++){
		int u , v;
		cin >> u >> v;
		u--;
		v--;
		g[u].push_back(v);
		g[v].push_back(u);
	}

	for(int i = 0 ; i < n ; i++)
		cin >> sit[i];

	for(int i = 0 ; i < n ; i++)
		for(int j = 0 ; j < 2 ; j++)
			for(int k = 0 ; k < 2 ; k++)
				dp[i][j][k] = INF;

	for(int i = 0 ; i < n ; i++)
		if((int)g[i].size() > 1)
			root = i;

	dfs(root , -1);

	int ans = min(dp[root][0][1] , dp[root][0][0]);
	if(ans > n) cout << "impossible" << '\n';
	else cout << ans << '\n';
	return 0;
}

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