Submission #677073

#	Time	Username	Problem	Language	Result	Execution time	Memory
677073		ajab_01	The Xana coup (BOI21_xanadu)	C++17	100 / 100	74 ms	19192 KiB

xanadu

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

#define int long long

const int N = 1e5 + 5;
const int INF = 1e12;
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;
	}

	int sum1 = 0 , sum2 = 0 , cnt1 = 0 , cnt2 = 0 , rem1 = INF , rem2 = INF;
	for(int i : g[ver]){
		if(i == par) continue;
		sum1 += min(dp[i][0][1] , dp[i][0][0]);
		sum2 += min(dp[i][1][1] , dp[i][1][0]);
		rem1 = min(rem1 , max(dp[i][0][1] , dp[i][0][0]) - min(dp[i][0][1] , dp[i][0][0]));
		rem2 = min(rem2 , max(dp[i][1][1] , dp[i][1][0]) - min(dp[i][1][1] , dp[i][1][0]));
		if(dp[i][0][1] <= dp[i][0][0]) cnt1++;
		if(dp[i][1][1] <= dp[i][1][0]) cnt2++; 
	}

	for(int k = 0 ; k < 2 ; k++){
		if(k == 1){
			dp[ver][sit[ver]][k] = min(dp[ver][sit[ver]][k] , sum2 + (cnt2 & 1 ? 0 : rem2) + 1);
			dp[ver][sit[ver] ^ 1][k] = min(dp[ver][sit[ver] ^ 1][k] , sum2 + (cnt2 & 1 ? rem2 : 0) + 1);
		}
		else{
			dp[ver][sit[ver]][k] = min(dp[ver][sit[ver]][k] , sum1 + (cnt1 & 1 ? rem1 : 0));
			dp[ver][sit[ver] ^ 1][k] = min(dp[ver][sit[ver] ^ 1][k] , sum1 + (cnt1 & 1 ? 0 : rem1));
		}
	}
}

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);
		if((int)g[v].size() > 1) root = v;
		if((int)g[u].size() > 1) root = 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;

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