Submission #1088885

#	Time	Username	Problem	Language	Result	Execution time	Memory
1088885		juicy	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	204 ms	76428 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif

const int N = 1e6;

int n, t, m;
int best[N], dep[N], dp[N];
bool flg[N];
vector<int> g[N];

void dfs(int u, int p) {
  if (u == t) {
    dp[u] = -dep[u];
    flg[u] = 1;
    return;
  }
  int c = -1, cnt = 0;
  for (int v : g[u]) {
    if (v ^ p) {
      dep[v] = dep[u] + 1;
      dfs(v, u);
      if (flg[v]) {
        flg[u] = 1;
        c = v;
      } else {
        ++cnt;
      }
    }
  }
  priority_queue<int, vector<int>, greater<int>> pq;
  for (int v : g[u]) {
    if (v == p) {
      continue;
    }
    if (~c && v ^ c) {
      dp[v] -= 2 * dep[u];
    }
    pq.push(dp[v]);
    if (pq.size() > 2) {
      pq.pop();
    }
  }
  if (!pq.size()) {
    dp[u] = dep[u];
    return;
  }
  if (pq.size() == 1) {
    dp[u] = ~c ? pq.top() : dep[u];
    return;
  }
  dp[u] = pq.top() + cnt - 1;
}

int main() {
  ios::sync_with_stdio(false); cin.tie(nullptr);

  cin >> n >> t >> m; --t; --m;
  for (int i = 1; i < n; ++i) {
    int u, v; cin >> u >> v; --u, --v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs(m, m);
  cout << dp[m] + dep[t];
  return 0;
}

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