Submission #403941

#	Time	Username	Problem	Language	Result	Execution time	Memory
403941		Nordway	The Xana coup (BOI21_xanadu)	C++17	0 / 100	140 ms	14936 KiB

xanadu

#include<bits/stdc++.h>

#define pb push_back

using namespace std;

const int N = 1e5 + 1;
const int inf = 1e9;

bool turned[N];

vector <int> g[N];

int dp[N][2][2];

void dfs(int v, int p) {
	for (int to : g[v]) {
		if (to != p) {
			dfs(to, v);
		}
	}
	int sum = 0;
	bool flip = 0;
	dp[v][0][0] = inf;
	dp[v][0][1] = inf;
	dp[v][1][0] = inf;
	dp[v][1][1] = inf;
	for (int to : g[v]) {
		if (to != p) {
			if (dp[to][0][0] == inf && dp[to][0][1] == inf) {
				sum = inf;
				break;
			}
			if (dp[to][0][0] == inf) sum += dp[to][0][1], flip ^= 1;
			if (dp[to][0][1] == inf) sum += dp[to][0][0];
		}
	}
	dp[v][turned[v] ^ flip][0] = min(dp[v][turned[v] ^ flip][0], sum);
	sum = 0;
	flip = 1;
	for (int to : g[v]) {
		if (to != p) {
			if (dp[to][1][0] == inf && dp[to][1][1] == inf) {
				sum = inf;
				break;
			}
			if (dp[to][1][0] == inf) sum += dp[to][1][1], flip ^= 1;
			if (dp[to][1][1] == inf) sum += dp[to][1][0];
		}
	}
	dp[v][turned[v] ^ flip][1] = min(dp[v][turned[v] ^ flip][1], sum + 1);
}

int main(){
	int n;
	cin >> n;

	for (int i = 1; i < n; i++) {
		int u, v;
		cin >> u >> v;
		g[u].pb(v);
		g[v].pb(u);
	}

	for (int i = 1; i <= n; i++) {
		cin >> turned[i];
	}

	dfs(1, 1);

	int ans = min(dp[1][0][0], dp[1][0][1]);
	if (ans == inf) cout << "impossible";
	else cout << ans;
}

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