Submission #1248044

#	Time	Username	Problem	Language	Result	Execution time	Memory
1248044		chuchucharles	Railway (BOI17_railway)	C++20	36 / 100	51 ms	25280 KiB

railway

#include <bits/stdc++.h>
using namespace std;
#define pii pair <int, int>
#define fi first
#define se second
const int maxn = 1e5 + 5;
int n, m, k, id[maxn], timer;
vector <int> adj[maxn], ans;
int dep[maxn], up[maxn][20], delta[maxn];
int in[maxn], out[maxn];
pii edges[maxn];

void dfs(int u, int p) {
    up[u][0] = p;
    for (int i = 1; i < 20; i++)
        up[u][i] = up[ up[u][i-1] ][i-1];
    in[u] = ++timer;
    for (int v : adj[u]) {
        if (v == p) continue;
        dep[v] = dep[u] + 1;
        dfs(v, u);
    }
    out[u] = timer;
}

int lca(int u, int v) {
    if (dep[u] < dep[v]) swap(u, v);
    int diff = dep[u] - dep[v];
    for (int i = 0; i < 20; i++) if (diff >> i & 1) u = up[u][i];
    if (u == v) return u;
    for (int i = 19; i >= 0; i--) if (up[u][i] != up[v][i]) {
        u = up[u][i];
        v = up[v][i];
    }
    return up[u][0];
}

int dfs2(int u, int p) {
    for (int v : adj[u]) if (v != p) {
        int t = dfs2(v, u);
        if (t >= k) ans.push_back(id[v]);
        delta[u] += t;
    }
    return delta[u];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m >> k;
    for (int i = 1, u, v; i < n; i++) {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
        edges[i] = {u, v};
    }
    dep[1] = 0;
    dfs(1, 0);
    for (int i = 1; i < n; i++) {
        int u = edges[i].fi, v = edges[i].se;
        if (dep[u] > dep[v]) id[u] = i;
        else id[v] = i;
    }
    for (int i = 0, x; i < m; i++) {
        cin >> x;
        vector<int> vc;
        vc.clear();
        for (int j = 0, u; j < x; j++) {
            cin >> u;
            vc.push_back (u);
        }
        sort(vc.begin(), vc.end(), [&](int a, int b){ return in[a] < in[b]; });
        for (int j = 1; j < x; j++) {
            int u = vc[j-1], v = vc[j];
            int w = lca(u, v);
            delta[u]++;
            delta[v]++;
            delta[w] -= 2;
        }
    }
    dfs2(1, 0);
    sort(ans.begin(), ans.end());
    cout << ans.size() << '\n';
    for (int i : ans) cout << i << ' ';
    return 0;
}

• Subtask 1: 0 / 8
• Subtask 2: 0 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 0 / 16
• Subtask 6: 0 / 25