Submission #1199418

#	Time	Username	Problem	Language	Result	Execution time	Memory
1199418		julia_08	Railway (BOI17_railway)	C++20	0 / 100	38 ms	23200 KiB

railway

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

const int MAXN = 1e5 + 10;

int dp[20][MAXN], sum[MAXN];

int pre[MAXN], pos[MAXN];

vector<int> adj[MAXN];

int t = 0;

void dfs_0(int v, int p){

  pre[v] = ++t;

  for(auto u : adj[v]){
    if(u != p){
      dp[0][u] = v;
      dfs_0(u, v);
    }
  }

  pos[v] = t;
}

void dfs_1(int v, int p){

  for(auto u : adj[v]){
    if(u != p){
      dfs_1(u, v);
      sum[v] += sum[u];
    }
  }

}

int sub(int a, int b){
  return pre[b] <= pre[a] && pos[a] <= pos[b];
}

int lca(int a, int b){

  if(sub(b, a)) return a;
  if(sub(a, b)) return b;

  for(int k=19; k>=0; k--){
    if(!sub(dp[k][b], a)){
      b = dp[k][b];
    }
  }

  return dp[0][b];
}

int main(){
  cin.tie(0)->sync_with_stdio(0);

  int n, m, k; cin >> n >> m >> k;

  vector<pair<int, int>> edges;

  for(int i=1; i<n; i++){

    int a, b; cin >> a >> b;

    edges.push_back({a, b});

    adj[a].push_back(b);
    adj[b].push_back(a);

  }

  dp[0][1] = 1;
  dfs_0(1, 1);

  for(int k=1; k<20; k++){
    for(int i=1; i<=n; i++){
      dp[k][i] = dp[k - 1][dp[k - 1][i]];
    }
  }

  while(m--){

    int s; cin >> s;

    vector<pair<int, int>> vtx(s);

    for(int i=0; i<s; i++){
      cin >> vtx[i].second;
      vtx[i].first = pre[vtx[i].second];
    }

    sort(vtx.begin(), vtx.end());

    vtx.push_back(vtx[0]);

    for(int i=1; i<=s; i++){

      int c = lca(vtx[i - 1].second, vtx[i].second);

      sum[c] --;
      sum[dp[0][c]] --;

      sum[vtx[i - 1].second] ++;
      sum[vtx[i].second] ++;

    }

  }

  dfs_1(1, 1);

  vector<int> ans;

  for(int i=0; i<(int) edges.size(); i++){
    if(sum[edges[i].first] >= 2 * k && sum[edges[i].second] >= 2 * k){
      ans.push_back(i + 1);
    }
  }

  cout << (int) ans.size() << "\n";

  for(auto x : ans) cout << x << " ";

  cout << "\n";

  return 0;
}

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