Submission #135175

#	Time	Username	Problem	Language	Result	Execution time	Memory
135175		fredbr	Beads and wires (APIO14_beads)	C++17	28 / 100	1054 ms	1276 KiB

beads

#include <bits/stdc++.h>
 
#pragma GCC optimize("O3")
 
using namespace std;
 
int const maxn = 10001;
 
struct Edge {
    int u, w;
};
 
vector<Edge> v[maxn];
int n;
int dp[2][maxn];
 
inline int invalid(int x) {
    return v[x].size() == 1;
}
 
int solve(int x, int p = -1, int t = 0) {
    if (dp[x][t] >= 0) return dp[x][t];
 
    int d = 0;
 
    if (t == 0) {
        for (Edge const& e : v[x]) {
            if (e.u == p) continue;
 
            if (!invalid(e.u)) {
                d += max(solve(e.u, x, 1) + e.w, solve(e.u, x, 0));
            }
        }
    }
    else {
        int sum = solve(x, p, 0);
 
        for (Edge const& e : v[x]) {
            if (e.u == p) continue;
 
            if (!invalid(e.u))
                d = max(d, sum - max(solve(e.u, x, 1) + e.w, solve(e.u, x, 0))
                           + e.w + solve(e.u, x, 0));
            else
                d = max(d, sum + e.w);
        }
    }
 
    return dp[x][t] = d;
}

char vis[maxn];
int res[maxn];

void bfs_order(int ini) {
    queue<int> q {{ini}};
    vis[ini] = 1;

    int at = 0;
    while (!q.empty()) {
        int x = q.front();
        res[at++] = x;
        q.pop();

        for (Edge const& e : v[x]) {
            if (vis[e.u]) continue;
            vis[e.u] = 1;
            q.push(e.u);
        }
    }
}


inline int test(int ini) {
    memset(vis, 0, sizeof(vis));
    bfs_order(ini);

    memset(vis, 0, sizeof(vis));

    for (int i = n-1; i >= 0; i--) {
        int x = res[i];
        vis[x] = 1;

        if (v[x].size() == 1 and x != ini) {
            dp[0][x] = 0, dp[1][x] = 0;
            continue;
        }

        int d = 0;
     
        for (Edge const& e : v[x]) {
            if (!vis[e.u]) continue;
 
            if (!invalid(e.u)) {
                d += max(dp[1][e.u] + e.w, dp[0][e.u]);
            }
        }
        dp[0][x] = d;

        d = 0;
        int sum = dp[0][x];
     
        for (Edge const& e : v[x]) {
            if (!vis[e.u]) continue;
 
            if (!invalid(e.u))
                d = max(d, sum - max(dp[1][e.u] + e.w, dp[0][e.u])
                           + e.w + dp[0][e.u]);
            else
                d = max(d, sum + e.w);
        }

        dp[1][x] = d;
    }

    return dp[0][ini];
}
 
int main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
 
    cin >> n;
 
    for (int i = 0; i < n-1; i++) {
        int a, b, w;
        cin >> a >> b >> w;
 
        v[a].push_back({b, w});
        v[b].push_back({a, w});
    }
 
    int ans = 0;
    for (int i = 1; i <= n; i++)
        if (v[i].size() == 1)
            ans = max(ans, test(i));
 
    cout << ans << "\n";
}

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43