Submission #916296

#	Time	Username	Problem	Language	Result	Execution time	Memory
916296		Alcabel	Beads and wires (APIO14_beads)	C++17	100 / 100	154 ms	26308 KiB

beads

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

const int maxn = 2e5;
const long long inf = 1e13;
vector<pair<int, int>> g[maxn];
long long dp[maxn][2];

void dfsCalc(int v, int p) {
    dp[v][0] = 0, dp[v][1] = -inf;
    for (const auto& [u, w] : g[v]) {
        if (u != p) {
            dfsCalc(u, v);
            dp[v][0] += max(dp[u][0], dp[u][1] + w);
        }
    }
    for (const auto& [u, w] : g[v]) {
        if (u != p) {
            dp[v][1] = max(dp[v][1], dp[v][0] - max(dp[u][0], dp[u][1] + w) + dp[u][0] + w);
        }
    }
}

long long up[maxn][2];

long long dfsAns(int v, int p, int pw) {
    long long ans, whole;
    ans = whole = dp[v][0] + max(up[v][0], up[v][1] + pw);
    pair<long long, int> max1 = {-inf, -2}, max2 = {-inf, -2}, cur;
    if (p != -1) {
        cur = {-max(up[v][0], up[v][1] + pw) + up[v][0] + pw, -1};
        if (cur >= max1) {
            max2 = max1, max1 = cur;
        } else if (cur > max2) {
            max2 = cur;
        }
    }
    for (const auto& [u, w] : g[v]) {
        if (u != p) {
            cur = {-max(dp[u][0], dp[u][1] + w) + dp[u][0] + w, u};
            if (cur >= max1) {
                max2 = max1, max1 = cur;
            } else if (cur > max2) {
                max2 = cur;
            }
        }
    }
    for (const auto& [u, w] : g[v]) {
        if (u != p) {
            up[u][0] = whole - max(dp[u][0], dp[u][1] + w);
            if (max1.second != u) {
                up[u][1] = up[u][0] + max1.first;
            } else {
                up[u][1] = up[u][0] + max2.first;
            }
            ans = max(ans, dfsAns(u, v, w));
        }
    }
    return ans;
}

void solve() {
    int n;
    cin >> n;
    for (int i = 0; i < n - 1; ++i) {
        int v, u, w;
        cin >> v >> u >> w;
        --v, --u;
        g[v].emplace_back(u, w);
        g[u].emplace_back(v, w);
    }
    dfsCalc(0, -1);
    up[0][0] = up[0][1] = 0;
    cout << dfsAns(0, -1, 0) << '\n';
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int T = 1;
    cin >> T;
    while (T--) {
        solve();
        cerr << "-----------\n";
        cout << "-----------\n";
    }
#else
    int T = 1;
    // cin >> T;
    while (T--) {
        solve();
    }
#endif

    return 0;
}

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