Submission #1291458

#	Time	Username	Problem	Language	Result	Execution time	Memory
1291458		hxian	Railway (BOI17_railway)	C++20	100 / 100	127 ms	49224 KiB

railway

// dmoj problem: https://vjudge.net/contest/765976#problem/G
#include <bits/stdc++.h>
#define int long long
#define all(x) x.begin(), x.end()
using namespace std;

int n, m, k, depth[100001], val[100001], parent[100001][20], start[100001], order[100001];
int cur;
vector<int> adjList[100001], special[100001];
vector<int> edges;
map<pair<int, int>, int> tracks;
void setdepth(int node, int last)
{
    order[node] = cur++;
    depth[node] = depth[last] + 1;
    parent[node][0] = last;
    for (int u : adjList[node])
        if (u != last)
            setdepth(u, node);
}
int lca(int a, int b)
{
    for (int i = 19; i >= 0; i--)
    {
        if (depth[a] - depth[b] >= (1 << i))
            a = parent[a][i];
        if (depth[b] - depth[a] >= (1 << i))
            b = parent[b][i];
    }
    if (a == b)
        return a;
    for (int i = 19; i >= 0; i--)
    {
        if (parent[a][i] != parent[b][i])
        {
            a = parent[a][i];
            b = parent[b][i];
        }
    }
    return parent[a][0];
}
int dfs(int node, int last)
{
    int sum = val[node];
    for (int u : adjList[node])
        if (u != last)
            sum += dfs(u, node);
    if (sum / 2 >= k)
    {
        edges.push_back(tracks[{min(node, last), max(node, last)}]);
    }
    return sum;
}
int32_t main()
{
    cin.sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> m >> k;
    for (int i = 1; i < n; i++)
    {
        int a, b;
        cin >> a >> b;
        adjList[a].push_back(b);
        adjList[b].push_back(a);
        tracks[{min(a, b), max(a, b)}] = i;
    }
    setdepth(1, 0);
    for (int i = 1; i < 20; i++)
        for (int j = 1; j <= n; j++)
            parent[j][i] = parent[parent[j][i - 1]][i - 1];
    for (int i = 0; i < m; i++)
    {
        int s;
        cin >> s;
        deque<int> specials;
        for (int j = 0; j < s; j++)
        {
            int a;
            cin >> a;
            specials.push_back(a);
            special[a].push_back(i);
        }
        sort(all(specials), [](int a, int b)
             { return order[a] < order[b]; });
        int ofall = specials[0];
        for (int i = 1; i < specials.size(); i++)
            ofall = lca(ofall, specials[i]);
        specials.push_front(ofall);
        for (int i = 0; i < specials.size(); i++)
        {
            int l = lca(specials[i], specials[(i + 1) % specials.size()]);
            val[l] -= 2;
            ++val[specials[i]];
            ++val[specials[(i + 1) % specials.size()]];
        }
    }
    dfs(1, 0);
    cout << edges.size() << "\n";
    sort(all(edges));
    for (int u : edges)
        cout << u << " ";
    cout << "\n";

    return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 16 / 16
• Subtask 6: 25 / 25