제출 #586366

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
586366		MilosMilutinovic	Torrent (COI16_torrent)	C++14	100 / 100	501 ms	29424 KiB

torrent

/**
 *    author:  wxhtzdy
 *    created: 30.06.2022 09:34:28
**/
#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);  
  int n, a, b;
  cin >> n >> a >> b;
  --a; --b;
  vector<vector<int>> g(n);
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    --u; --v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  vector<int> par(n);
  function<void(int, int)> Dfs = [&](int v, int pr) {
    par[v] = pr;
    for (int u : g[v]) {
      if (u != pr) {
        Dfs(u, v);
      }
    }
  };
  Dfs(a, a);
  vector<int> path;
  int x = b;
  while (x != a) {
    path.push_back(x);
    x = par[x];
  }
  pair<int, int> f;
  vector<int> dp(n);
  Dfs = [&](int v, int pr) {
    vector<int> ch;
    for (int u : g[v]) {
      if (u == pr || make_pair(u, v) == f || make_pair(v, u) == f) {
        continue;
      }
      Dfs(u, v);
      ch.push_back(u);
    }
    dp[v] = 0;
    sort(ch.begin(), ch.end(), [&](int i, int j) {
      return dp[i] > dp[j];
    });
    for (int i = 0; i < (int) ch.size(); i++) {
      dp[v] = max(dp[v], dp[ch[i]] + i + 1);
    }
  };
  auto Solve = [&](int root, int id) {
    f = make_pair(path[id], par[path[id]]);
    Dfs(root, root);
    return dp[root];
  };
  int sz = (int) path.size();
  int low = 0, high = sz - 1;
  while (low < high) {
    int mid = (low + high) >> 1;
    if (Solve(a, mid) <= Solve(b, mid)) {
      high = mid;
    } else {
      low = mid + 1;
    }
  }        
  int ans = 1e9;
  for (int i = -1; i <= 1; i++) {
    if (low + i >= 0 && low + i < sz) {
      ans = min(ans, max(Solve(a, low + i), Solve(b, low + i)));
    }
  }
  cout << ans <<  '\n';
  return 0;
}

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69