Submission #468697

#	Time	Username	Problem	Language	Result	Execution time	Memory
468697		paga2004	Mousetrap (CEOI17_mousetrap)	C++14	0 / 100	389 ms	78596 KiB

mousetrap

#include <bits/stdc++.h>

#define int long long

using namespace std;

#ifdef LOCAL
#define dbg(x) cerr << x << "\n";
#else
#define dbg(x)
#endif

const int INF = 1e17;

int n, t, m;
vector<int> scores;
vector<vector<int>> g;
vector<int> depths;

int dfs1(int v, int p) {
  depths[v] = depths[p] + 1;
  vector<int> besties;
  for (int w : g[v]) {
    if (w == p)
      continue;
    besties.push_back(dfs1(w, v));
  }
  sort(besties.begin(), besties.end());
  int score = max((int)g[v].size() - 1, 1ll);
  if (besties.size() >= 2) {
    score += besties[besties.size() - 2];
  }
  return scores[v] = score;
}

int dfs2(int v, int p, int blocks) {
  dbg("v " << v << " blocks " << blocks);
  int score = INF;
  if (v == m) {
    return blocks + scores[v];
  }
  blocks += g[v].size() - 2;
  for (int w : g[v]) {
    if (w == p)
      continue;
    score = min(dfs2(w, v, blocks), score);
    dbg("current score: " << score);
  }
  if (v == t)
    return score;
  if (score != INF) {
    return min(score, blocks - 1 + scores[v]);
  }
  return INF;
}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  cin >> n >> t >> m;
  t--;
  m--;
  g.resize(n);
  scores.resize(n);
  depths.resize(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    g[a].push_back(b);
    g[b].push_back(a);
  }

  depths[t] = 0;
  dfs1(t, t);

  cout << dfs2(t, t, -g[t].size() + 2) << "\n";
}

• Subtask 1: 0 / 20
• Subtask 2: 0 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35