Submission #759039

#	Time	Username	Problem	Language	Result	Execution time	Memory
759039		gnu	The Xana coup (BOI21_xanadu)	C++14	100 / 100	171 ms	33460 KiB

xanadu

#include <iostream>
#include <vector>
using namespace std;
using ll = long long;
vector<vector<vector<ll>>> dp;
vector<int> state;
void dfs(int u, int p, vector<vector<int>>& gp)
{
	ll sum1 = 0, cnt1 = 0, mn1 = 1e18, sum2 = 0, cnt2 = 0, mn2 = 1e18;
	for (int v : gp[u]) {
		if (v == p) continue;
 
		dfs(v, u, gp);
		if (dp[v][1][0] < dp[v][0][0]) {
			sum1 += dp[v][1][0];
			++cnt1;
		}
		else {
			sum1 += dp[v][0][0];
		}
		mn1 = min(mn1, abs(dp[v][1][0] - dp[v][0][0]));
		if (dp[v][1][1] < dp[v][0][1]) {
			sum2 += dp[v][1][1];
			++cnt2;
		}
		else {
			sum2 += dp[v][0][1];
		}
		mn2 = min(mn2, abs(dp[v][1][1] - dp[v][0][1]));
 
	}
	if (gp[u].size() == 1 && u != 0) {
		if (state[u]) {
			dp[u][1][0] = 1;
			dp[u][0][0] = 1e18;
			dp[u][1][1] = 1e18;
			dp[u][0][1] = 0;
		}
		else {
			dp[u][1][0] = 1e18;
			dp[u][0][0] = 0;
			dp[u][1][1] = 1;
			dp[u][0][1] = 1e18;
		}
		return;
	}
	if (((cnt1 & 1) && state[u]) || (!(cnt1 & 1) && !state[u])) {
		dp[u][0][0] = sum1;
	}
	else {
		dp[u][0][0] = sum1 + mn1;
	}
	state[u] = !state[u];
	if (((cnt2 & 1) && state[u]) || (!(cnt2 & 1) && !state[u])) {
		dp[u][1][0] = sum2+1;
	}
	else {
		dp[u][1][0] = sum2 + mn2+1;
	}
 
 
	if (((cnt1 & 1) && state[u]) || (!(cnt1 & 1) && !state[u])) {
		dp[u][0][1] = sum1;
	}
	else {
		dp[u][0][1] = sum1 + mn1;
	}
 
	state[u] = !state[u];
	if (((cnt2 & 1) && state[u]) || (!(cnt2 & 1) && !state[u])) {
		dp[u][1][1] = sum2+1;
	}
	else {
		dp[u][1][1] = sum2 + mn2+1;
	}
    dp[u][0][0] = min(dp[u][0][0], (long long) 1e18);
    dp[u][1][0] = min(dp[u][1][0], (long long) 1e18);
    dp[u][1][1] = min(dp[u][1][1], (long long) 1e18);
    dp[u][0][1] = min(dp[u][0][1], (long long) 1e18);
 
}
 
void solve()
{
	int n; cin >> n;
	vector<vector<int>> gp(n);
	state = vector<int>(n);
	dp = vector<vector<vector<ll>>>(n, vector<vector<ll>>(2, vector<ll>(2)));
	for (int i = 0; i < n - 1; ++i) {
		int u, v; cin >> u >> v; --u; --v;
		gp[u].push_back(v);
		gp[v].push_back(u);
	}
	for (int& x : state) {cin >> x;}
	dfs(0, -1, gp);
	if (min(dp[0][0][0], dp[0][1][0]) <= n) {
		cout << min(dp[0][0][0], dp[0][1][0]) << '\n';
	}
	else {
		cout <<"impossible\n";
	}
 
 
}
int main()
{
	//int t; cin >> t; while (t--)
		solve();
}

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