Submission #987810

#	Time	Username	Problem	Language	Result	Execution time	Memory
987810		MilosMilutinovic	Love Polygon (BOI18_polygon)	C++14	100 / 100	281 ms	34248 KiB

polygon

#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  vector<int> to(n);
  map<string, int> mp;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    string t;
    cin >> t;
    if (!mp.count(s)) {
      mp[s] = (int) mp.size();
    }
    if (!mp.count(t)) {
      mp[t] = (int) mp.size();
    }
    to[mp[s]] = mp[t];
  }
  if (n % 2 == 1) {
    cout << -1 << '\n';
    return 0;
  }
  vector<vector<int>> ch(n);
  for (int i = 0; i < n; i++) {
    if (to[i] == i) {
      continue;
    }
    ch[to[i]].push_back(i);
  }
  vector<int> deg(n);
  for (int i = 0; i < n; i++) {
    deg[to[i]] += 1;
  }
  vector<int> que;
  for (int i = 0; i < n; i++) {
    if (deg[i] == 0) {
      que.push_back(i);
    }
  }
  for (int b = 0; b < (int) que.size(); b++) {
    int i = que[b];
    deg[to[i]] -= 1;
    if (deg[to[i]] == 0) {
      que.push_back(to[i]);
    }
  }
  vector<vector<int>> dp(n, vector<int>(2));
  vector<int> comp;
  function<void(int, int)> Solve = [&](int v, int ban) {
    comp.push_back(v);
    int mx = 0;
    for (int u : ch[v]) {
      Solve(u, ban);
      dp[v][0] += max(dp[u][0], dp[u][1]);
      dp[v][1] += max(dp[u][0], dp[u][1]);
      if (u != ban) {
        mx = max(mx, -max(dp[u][0], dp[u][1]) + dp[u][0] + 1);
      }
    }
    dp[v][1] += mx;
    if (v == ban) {
      dp[v][1] = 0;
    }
  };
  int res = 0;
  for (int i = 0; i < n; i++) {
    if (deg[i] == 0) {
      continue;
    }
    if (to[i] == i) {
      Solve(i, -1);
      res += max(dp[i][1], dp[i][0]); 
    } else if (i == to[to[i]]) {
      deg[i] = 0;
      deg[to[i]] = 0;
      {
        vector<int> new_ch;
        for (int x : ch[i]) {
          if (x == to[i]) {
            continue;
          }
          new_ch.push_back(x);
        }
        ch[i] = new_ch;
      }
      {
        vector<int> new_ch;
        for (int x : ch[to[i]]) {
          if (x == i) {
            continue;
          }
          new_ch.push_back(x);
        }
        ch[to[i]] = new_ch;
      }
      Solve(i, -1);
      Solve(to[i], -1);
      res += max(max(dp[i][0], dp[i][1]) + max(dp[to[i]][0], dp[to[i]][1]), dp[i][0] + dp[to[i]][0] + 2);
    } else {
      vector<int> new_ch;
      for (int x : ch[to[i]]) {
        if (x == i) {
          continue;
        }
        new_ch.push_back(x);
      }
      ch[to[i]] = new_ch;
      int prv = to[i];
      to[i] = i;
      comp.clear();
      Solve(i, -1);
      int c = max(dp[i][0], dp[i][1]);
      for (int x : comp) {
        dp[x][0] = 0;
        dp[x][1] = 0;
        deg[x] = 0;
      }
      Solve(i, prv);
      c = max(c, dp[i][0] + 1);
      res += c;
    }
  }
  cout << (n - 2 * res) + res << '\n';
  return 0;
}

• Subtask 1: 21 / 21
• Subtask 2: 25 / 25
• Subtask 3: 29 / 29
• Subtask 4: 25 / 25