Submission #557681

#	Time	Username	Problem	Language	Result	Execution time	Memory
557681		Jomnoi	Beads and wires (APIO14_beads)	C++17	100 / 100	315 ms	33268 KiB

beads

#include <bits/stdc++.h>
using namespace std;

const int MAX_N = 2e5 + 5;
const int INF = 1e9 + 7;

int N;
int ans;
vector <pair <int, int>> graph[MAX_N];
int dp[MAX_N][2], pdp[MAX_N];

void dfs(int u, int p) {
    dp[u][1] = -INF;
    for(auto [v, w] : graph[u]) {
        if(v == p) {
            continue;
        }

        dfs(v, u);

        dp[u][0] += max(dp[v][0], dp[v][1] + w);
    }

    for(auto [v, w] : graph[u]) {
        if(v == p) {
            continue;
        }

        dp[u][1] = max(dp[u][1], dp[u][0] - max(dp[v][0], dp[v][1] + w) + dp[v][0] + w);
    }
}

void dfs2(int u, int p, int pw) {
    ans = max(ans, dp[u][0] + pdp[u]);

    multiset <int> siblings;
    for(auto [v, w] : graph[u]) {
        if(v == p) {
            continue;
        }

        siblings.insert(dp[v][0] + w - max(dp[v][0], dp[v][1] + w));
        pdp[v] = max(pdp[v], dp[u][0] - max(dp[v][0], dp[v][1] + w) + pdp[u]);
        if(p != -1) {
            pdp[v] = max(pdp[v], w + pw + dp[u][0] - max(dp[v][0], dp[v][1] + w) + pdp[p] + dp[p][0] - max(dp[u][0], dp[u][1] + pw));
        }
    }

    if(siblings.size() > 1) {
        for(auto [v, w] : graph[u]) {
            if(v == p) {
                continue;
            }

            siblings.erase(siblings.lower_bound(dp[v][0] + w - max(dp[v][0], dp[v][1] + w)));
            pdp[v] = max(pdp[v], pdp[u] + dp[u][0] + w - max(dp[v][0], dp[v][1] + w) + *siblings.rbegin());
            siblings.insert(dp[v][0] + w - max(dp[v][0], dp[v][1] + w));
        }
    }

    for(auto [v, w] : graph[u]) {
        if(v != p) {
            dfs2(v, u, w);
        }
    }
}

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    cin >> N;
    for(int i = 1; i <= N - 1; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        graph[a].emplace_back(b, c);
        graph[b].emplace_back(a, c);
    }

    dfs(1, -1);
    dfs2(1, -1, -INF);

    cout << ans;
    return 0;
}

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