Submission #1055716

#	Time	Username	Problem	Language	Result	Execution time	Memory
1055716		GrandTiger1729	Beads and wires (APIO14_beads)	C++17	100 / 100	81 ms	34616 KiB

beads

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

const int INF = 2e9 + 10;
int main()
{
    cin.tie(0)->sync_with_stdio(0);
    int n;
    cin >> n;
    vector<vector<pair<int, int>>> g(n);
    for (int i = 0; i < n - 1; i++)
    {
        int u, v, w;
        cin >> u >> v >> w;
        u--, v--;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
    }
    vector<bool> vis(n);
    vector<vector<int>> dp(n, vector<int>(4, -INF));
    function<void(int, int)> dfs = [&](int u, int W)
    {
        vis[u] = true;
        dp[u][0] = dp[u][2] = 0;
        vector<int> res;
        for (auto &[v, w] : g[u])
        {
            if (!vis[v])
            {
                dfs(v, w);
                dp[u][0] += max(dp[v][0], dp[v][1]);
                res.push_back(dp[v][0] + w - max(dp[v][0], dp[v][1]));
            }
        }
        sort(begin(res), end(res), greater<>());
        if (res.size() >= 1)
        {
            dp[u][1] = dp[u][0] + W + res[0];
            for (auto &[v, w] : g[u])
            {
                if (!vis[v])
                {
                    dp[u][2] = max(dp[u][2], max(dp[v][2], dp[v][3]) - max(dp[v][0], dp[v][1]) + dp[u][0]);
                    dp[u][3] = max(dp[u][3], dp[v][2] + w + W - max(dp[v][0], dp[v][1]) + dp[u][0]);
                }
            }
        }
        if (res.size() >= 2)
        {
            for (auto &[v, w] : g[u])
            {
                if (!vis[v])
                {
                    int x = dp[v][0] + w - max(dp[v][0], dp[v][1]) == res[0] ? res[1] : res[0];
                    dp[u][2] = max(dp[u][2], dp[u][0] + dp[v][2] + w - max(dp[v][0], dp[v][1]) + x);
                }
            }
        }
        dp[u][2] = max(dp[u][2], dp[u][0]);
        dp[u][3] = max(dp[u][3], dp[u][1]);
        vis[u] = false;
    };
    dfs(0, -INF);
    int ans = max(dp[0][2], dp[0][3]);
    cout << ans << '\n';
    return 0;
}

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