Submission #467072

#	Time	Username	Problem	Language	Result	Execution time	Memory
467072		MVP_Harry	The Xana coup (BOI21_xanadu)	C++17	100 / 100	100 ms	21984 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define rep(i, m, n) for (int i = m; i <= n; i++)
#define per(i, m, n) for (int i = m; i >= n; i--)
#define sz(v) (int) v.size()
#define all(v) v.begin(), v.end()
#define ll long long
#define pb push_back
#define mp make_pair
#define fi first
#define se second

const int maxn = 1e5 + 5;

int N;
ll dp[maxn][2][2], a[maxn];
vector<int> G[maxn];

void dfs(int u, int k) {
	ll sum1 = 0, sum2 = 0, mn1 = 1e18, mn2 = 1e18, cnt1 = 0, cnt2 = 0;
	for (auto v : G[u]) {
		if (v == k) continue;
		dfs(v, u);
		sum1 += min(dp[v][0][0], dp[v][0][1]);
		mn1 = min(mn1, abs(dp[v][0][0] - dp[v][0][1]));
		if (dp[v][0][1] < dp[v][0][0]) cnt1++;
		sum2 += min(dp[v][1][0], dp[v][1][1]);
		mn2 = min(mn2, abs(dp[v][1][0] - dp[v][1][1]));
		if (dp[v][1][1] < dp[v][1][0]) cnt2++;
	}
	if ((cnt1 + a[u]) % 2 == 0) {
		dp[u][0][0] = min(dp[u][0][0], sum1);
		dp[u][1][0] = min(dp[u][1][0], sum1 + mn1);
	} else {
		dp[u][0][0] = min(dp[u][0][0], sum1 + mn1);
		dp[u][1][0] = min(dp[u][1][0], sum1);
	}
	if ((cnt2 + a[u]) % 2 == 1) {
		dp[u][0][1] = min(dp[u][0][1], sum2 + 1);
		dp[u][1][1] = min(dp[u][1][1], sum2 + mn2 + 1);
	} else {
		dp[u][0][1] = min(dp[u][0][1], sum2 + mn2 + 1);
		dp[u][1][1] = min(dp[u][1][1], sum2 + 1);
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> N;
	rep(i, 1, N - 1) {
		int u, v;
		cin >> u >> v;
		G[u].pb(v), G[v].pb(u);
	}
	rep(i, 1, N) cin >> a[i];
	rep(i, 1, N) rep(j, 0, 1) rep(k, 0, 1) dp[i][j][k] = 1e9;
	dfs(1, 0);
	ll ans = min(dp[1][0][0], dp[1][0][1]);
	if (ans == (ll) 1e9) {
		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