Submission #506386

#	Time	Username	Problem	Language	Result	Execution time	Memory
506386		Elegia	The Xana coup (BOI21_xanadu)	C++17	100 / 100	73 ms	16904 KiB

xanadu

#include <bits/stdc++.h>

using ull = unsigned long long;

using namespace std;

const int P = 998244353;

int norm(int x) { return x >= P ? x - P : x; }
int reduce(int x) { return x < 0 ? x + P : x; }
int neg(int x) { return x ? P - x : 0; }
void add(int& x, int y) { if ((x += y - P) < 0) x += P; }
void sub(int& x, int y) { if ((x -= y) < 0) x += P; }
void fam(int& x, int y, int z) { x = (x + y * (ull)z) % P; }
int mpow(int x, unsigned k) {
	if (k == 0) return 1;
	int ret = mpow(x * (ull)x % P, k >> 1);
	if (k & 1) ret = ret * (ull)x % P;
	return ret;
}
int quo2(int x) { return ((x & 1) ? x + P : x) >> 1; }

const int _ = 100010;

vector<int> G[_];
int f[_], dp[_][2][2];

void dfs(int u, int p) {
	dp[u][0][f[u]] = 0; dp[u][1][f[u] ^ 1] = 1;
	dp[u][0][f[u] ^ 1] = dp[u][1][f[u]] = _;
	for (int v : G[u]) if (p != v) {
		dfs(v, u);
		static int tmp[2][2];
		for (int a = 0; a <= 1; ++a)
			for (int b = 0; b <= 1; ++b) {
				tmp[a][b] = _;
				for (int c = 0; c <= 1; ++c)
					tmp[a][b] = min(tmp[a][b], dp[u][a][b ^ c] + dp[v][c][a]);
			}
		memcpy(dp[u], tmp, sizeof(tmp));
	}
}

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

	int N; cin >> N;
	for (int rep = 1; rep != N; ++rep) {
		int u, v; cin >> u >> v;
		G[u].push_back(v); G[v].push_back(u);
	}
	for (int i = 1; i <= N; ++i) cin >> f[i];
	dfs(1, 0);
	int ans = min(dp[1][0][0], dp[1][1][0]);
	if (ans <= N) cout << ans << '\n';
	else cout << "impossible\n";

	return 0;
}

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