Submission #548120

#	Time	Username	Problem	Language	Result	Execution time	Memory
548120		lorenzoferrari	Islands (IOI08_islands)	C++17	0 / 100	2092 ms	131072 KiB

islands

#include <bits/stdc++.h>
using namespace std;
using LL = long long;

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

vector<bool> vis, cycle;
vector<array<LL, 2>> prv, nxt;
vector<LL> dl, dr;
vector<LL> f;

LL max_path(const vector<int>& c, const vector<vector<array<LL, 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, v);
      if (works) {
        nxt[v] = {u, w};
        prv[u] = {v, w};
        return cycle[v] ? false : cycle[v] = true;
      }
    }
    return false;
  };
  find_cycle(find_cycle, c[0]);
  LL dep = 0;
  auto path_in_tree = [&](auto&& self, int v, int p = -1) -> LL {
    while (dep++ > 10000) ;
    LL ans = 0;
    for (auto [u, w, eid] : adj[v]) {
      if (u == p || u == prv[v][0] || u == nxt[v][0]) continue;
      ans = max(ans, w + self(self, u, v));
    }
    return ans;
  };
  int start = -1;
  for (int i : c) {
    if (cycle[i]) {
      start = i;
      f[i] = path_in_tree(path_in_tree, i);
    }
  }
  return 42;
  // multiset<LL> L, R;
  // {
  //   int v = start;
  //   int u = start;
  //   dl[v] = dr[u] = 0;
  //   do {
  //     auto [nv, lw] = nxt[v];
  //     auto [nu, rw] = prv[u];
  //     if (v != start) L.insert(f[v] + dl[v]);
  //     if (u != start) R.insert(f[u] + dr[u]);
  //     if (nv != start) dl[nv] = dl[v] + lw;
  //     dr[nu] = dr[u] + rw;
  //     v = nv;
  //     u = nu;
  //   } while (v != start);
  // }
  // assert(dl[start] == 0);
  // LL len = dr[start];
  // LL bias = 0;
  // LL ans = 0;
  // {
  //   int v = start;
  //   do {
  //     // watch(v);
  //     // watch(bias);
  //     // cerr << "L: "; for (LL i : L) cerr << i << " "; cerr << endl;
  //     // cerr << "R: "; for (LL i : R) cerr << i << " "; cerr << endl;
  //     // cerr << endl;
  //     ans = max(ans, *prev(L.end()) - bias + f[v]);
  //     ans = max(ans, *prev(R.end()) + bias + f[v]);
  //     int nv = nxt[v][0];
  //     if (nv == start) break;
  //     bias += nxt[v][1];
  //     L.insert(f[v] + dl[v] + len);
  //     R.insert(f[v] + dr[v] - len);
  //     if (L.count(f[nv] + dl[nv])) L.erase(L.find(f[nv] + dl[nv]));
  //     if (R.count(f[nv] + dr[nv])) R.erase(R.find(f[nv] + dr[nv]));
  //     v = nv;
  //   } while (v != start);
  // }
  // return ans;
}

int main() {
#ifdef LORENZO
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  int n; cin >> n;
  vector<vector<array<LL, 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);
    }
  }
  f.assign(n, 0);
  dl.assign(n, 1e18);
  dr.assign(n, 1e18);
  prv.assign(n, {-1,-1});
  nxt.assign(n, {-1,-1});
  vis.assign(n, false);
  cycle.assign(n, false);
  LL ans = 0;
  for (const auto& c : cc) {
    ans += max_path(c, adj);
  }
  cout << ans << "\n";
}

Compilation message (stderr)

islands.cpp: In function 'LL max_path(const std::vector<int>&, const std::vector<std::vector<std::array<long long int, 3> > >&)':
islands.cpp:38:7: warning: variable 'start' set but not used [-Wunused-but-set-variable]
   38 |   int start = -1;
      |       ^~~~~

• Subtask 1: 0 / 33
• Subtask 2: 0 / 3
• Subtask 3: 0 / 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