Submission #548398

#	Time	Username	Problem	Language	Result	Execution time	Memory
548398		lorenzoferrari	Islands (IOI08_islands)	C++17	34 / 100	2082 ms	128044 KiB

islands

#include <bits/stdc++.h>
#pragma GCC optimize ("O3")
using namespace std;
using LL = long long;

#define watch(x) cerr << (#x) << " is " << x << endl

vector<bool> vis, cycle;
vector<array<int, 2>> nxt;

LL max_path(const vector<int>& c, const vector<vector<array<int, 3>>>& adj) {
  auto find_cycle = [&](auto&& self, int v, int pid = -1) -> bool {
    if (vis[v]) return cycle[v] = true;
    vis[v] = true;
    for (auto [u, w, eid] : adj[v]) {
      if (eid == pid) continue;
      bool works = self(self, u, eid);
      if (works) {
        nxt[v] = {u, w};
        return cycle[v] ? false : cycle[v] = true;
      }
    }
    return false;
  };
  find_cycle(find_cycle, c[0]);
  auto path_in_tree = [&](auto&& self, int v, int p = -1) -> LL {
    LL ans = 0;
    for (auto [u, w, eid] : adj[v]) {
      if (u == p || cycle[u]) continue;
      ans = max(ans, w + self(self, u, v));
    }
    return ans;
  };
  int start = -1;
  for (int i : c) if (cycle[i]) start = i;
  vector<LL> fs;
  vector<LL> ds;
  {
    int v = start;
    LL len = 0;
    do {
      fs.push_back(path_in_tree(path_in_tree, v));
      ds.push_back(len);
      auto [nv, lw] = nxt[v];
      len += lw;
      v = nv;
    } while (v != start);
    ds.push_back(len);
  }
  int n = fs.size();
  for (int i = 0; i < n; ++i) fs.push_back(fs[i]);
  for (int i = 1; i < n; ++i) ds.push_back(ds.back() + ds[i] - ds[i-1]);
  LL ans = 0;
/*
maximize {fs[i] + fs[j] + ds[j] - ds[i]}, with i < j < i+n
fs[i] - ds[i] + max(fs[j] + ds[j])
*/
  deque<array<LL, 2>> best;
  int until = -1;
  for (int i = 0; i < n; ++i) {
    for (int j = until+1; j < i+n; ++j) {
      while (!best.empty() && best.front()[1] <= i-n) best.pop_front();
      while (!best.empty() && best.back()[0] < fs[j]+ds[j]) best.pop_back();
      best.push_back({fs[j]+ds[j], j});
    }
    ans = max(ans, fs[i] - ds[i] + best.front()[0]);
  }
  return ans;
}

int32_t main() {
#ifdef LORENZO
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n; cin >> n;
  vector<vector<array<int, 3>>> adj(n);
  for (int i = 0; i < n; ++i) {
    int a; cin >> a; --a;
    int w; cin >> w;
    adj[i].push_back({a, w, i});
    adj[a].push_back({i, w, i});
  }
  vis.assign(n, false);
  vector<vector<int>> cc;
  auto dfs = [&](auto&& self, int v) -> void {
    vis[v] = true;
    cc.back().push_back(v);
    for (auto [u, _, __] : adj[v]) {
      if (!vis[u]) {
        self(self, u);
      }
    }
  };
  for (int i = 0; i < n; ++i) {
    if (!vis[i]) {
      cc.push_back(vector<int>(0));
      dfs(dfs, i);
    }
  }
  nxt.assign(n, {-1,-1});
  vis.assign(n, false);
  cycle.assign(n, false);
  LL ans = 0;
  for (auto& c : cc) {
    ans += max_path(c, adj);
    c.clear();
  }
  cout << ans << "\n";
}

• Subtask 1: 27 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10