Submission #453265

#	Time	Username	Problem	Language	Result	Execution time	Memory
453265		valerikk	Beads and wires (APIO14_beads)	C++17	100 / 100	412 ms	33416 KiB

beads

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>

using namespace std;

typedef long long ll;

const int N = 200010;
const int INF = 2e9;

int n;
vector<pair<int, int>> g[N];
int dp[N][2];
int up[N][2];
int ans = 0;

void dfs(int v, int p = -1, int pc = 0) {
	int mx = -INF, sum = 0;
	for (auto [u, c] : g[v]) {
		if (u != p) {
			dfs(u, v, c);
			sum += dp[u][1];
			mx = max(mx, dp[u][0] - dp[u][1] + c);
		}
	}
	dp[v][0] = sum;
	dp[v][1] = sum + max(0, mx + pc);
}

void go(int v, int p = -1, int pc = 0) {
	int sum = 0;
	multiset<int> st;
	if (p != -1) {
		sum += up[v][1];
		st.insert(up[v][0] - up[v][1] + pc);
	}
	for (auto [u, c] : g[v]) {
		if (u != p) {
			sum += dp[u][1];
			st.insert(dp[u][0] - dp[u][1] + c);
		}
	}
	ans = max(ans, sum);
	for (auto [u, c] : g[v]) {
		if (u != p) {
			sum -= dp[u][1];
			st.erase(st.find(dp[u][0] - dp[u][1] + c));
			up[u][0] = sum;
			up[u][1] = sum + (st.empty() ? 0 : max(0, *st.rbegin() + c));
			go(u, v, c);
			sum += dp[u][1];
			st.insert(dp[u][0] - dp[u][1] + c);
		}
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> n;
	for (int i = 0; i < n - 1; ++i) {
		int a, b, c;
		cin >> a >> b >> c;
		g[a].push_back({b, c});
		g[b].push_back({a, c});
	}
	dfs(1);
	go(1);
	cout << ans << endl;
	return 0;
}

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 43 / 43