Submission #537298

#	Time	Username	Problem	Language	Result	Execution time	Memory
537298		skittles1412	The Xana coup (BOI21_xanadu)	C++17	100 / 100	131 ms	22792 KiB

xanadu

#include "bits/extc++.h"

using namespace std;

template <typename T>
void dbgh(const T& t) {
	cerr << t << endl;
}

template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
	cerr << t << " | ";
	dbgh(u...);
}

#ifdef DEBUG
#define dbg(...)                                           \
	cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
		 << ": ";                                          \
	dbgh(__VA_ARGS__)
#else
#define cerr   \
	if (false) \
	cerr
#define dbg(...)
#endif

#define endl "\n"
#define long int64_t
#define sz(x) int((x).size())

const int maxn = 1e5 + 5;

bool arr[maxn];
int memo[maxn][2][2];
vector<int> graph[maxn];

void pdfs(int u) {
	for (auto& v : graph[u]) {
		graph[v].erase(find(begin(graph[v]), end(graph[v]), u));
		pdfs(v);
	}
}

int dp(int u, bool p, bool c) {
	int &ans = memo[u][p][c];
	if (ans != -1) {
		return ans;
	}
	int cdp[2];
	cdp[0] = cdp[1] = 1e9;
	cdp[p ^ c] = 0;
	for (auto& v : graph[u]) {
		int ndp[2];
		for (int i = 0; i < 2; i++) {
			ndp[i] = min({int(1e9), cdp[i] + dp(v, c, false), cdp[i ^ 1] + 1 + dp(v, c, true)});
		}
		cdp[0] = ndp[0];
		cdp[1] = ndp[1];
	}
	return ans = cdp[arr[u]];
}

void solve() {
	int n;
	cin >> n;
	for (int i = 0; i < n - 1; i++) {
		int u, v;
		cin >> u >> v;
		u--;
		v--;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	for (int i = 0; i < n; i++) {
		cin >> arr[i];
	}
	pdfs(0);
	memset(memo, -1, sizeof(memo));
	int ans = min(dp(0, false, false), 1 + dp(0, false, true));
	if (ans < int(1e9)) {
		cout << ans << endl;
	} else {
		cout << "impossible" << endl;
	}
}

int main() {
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	cin.exceptions(ios::failbit);
	solve();
}

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