Submission #940773

#	Time	Username	Problem	Language	Result	Execution time	Memory
940773		duckindog	Dreaming (IOI13_dreaming)	C++17	18 / 100	39 ms	14112 KiB

dreaming

#include <bits/stdc++.h>

using namespace std;

#ifndef LOCAL
#include "dreaming.h"
#endif

const int N = 100'000 + 10;
vector<pair<int, int>> ad[N];

bool mk[N];
int dpin[N], dpout[N];
void dfs1(int u, int p = 0) { 
  mk[u] = true;
  for (const auto& [v, w] : ad[u]) { 
    if (v == p) continue;
    dfs1(v, u);
    dpin[u] = max(dpin[u], dpin[v] + w);
  }
}
int dfs2(int u, int p = 0) { 
  array<pair<int, int>, 2> best;
  best[0] = best[1] = {-1e9, -1};
  
  auto add = [&](pair<int, int> x) { 
    if (best[1] < x) swap(best[1], x);
    if (best[0] < best[1]) swap(best[0], best[1]);
  };

  add({dpout[u], u});
  for (const auto& [v, w] : ad[u]) if (v != p) add({dpin[v] + w, v});

  int ret = u;
  for (const auto& [v, w] : ad[u]) { 
    if (v == p) continue;
    dpout[v] = (best[0].second == v ? best[1].first : best[0].first) + w;
    int nv = dfs2(v, u);
    if (max(dpin[nv], dpout[nv]) < max(dpin[ret], dpout[ret])) ret = nv;
  }
  return ret;
}

int travelTime(int n, int m, int l, int A[],int B[],int T[]) { 
  for (int i = 1; i <= m; ++i) { 
    int u = A[i], v = B[i], w = T[i];
    ad[u].push_back({v, w});
    ad[v].push_back({u, w});
  }
  
  vector<int> ed;
  for (int i = 1; i <= n; ++i) { 
    if (mk[i]) continue;
    dfs1(i);
    int x = dfs2(i);
    ed.push_back(max(dpin[x], dpout[x]));
  }
  sort(ed.begin(), ed.end(), greater<>());
  
  if (ed.size() == 1) return ed[0];
  if (ed.size() == 2) return ed[0] + ed[1] + l;
  if (ed.size() >= 3) return max(ed[0] + ed[1] + l, ed[1] + ed[2] + 2 * l);
}

#ifdef LOCAL
int n, m, l;
int A[N], B[N], T[N];
int32_t main() { 
  cin.tie(0)->sync_with_stdio(0);

  cin >> n >> m >> l;
  for (int i = 1; i <= m; ++i) cin >> A[i] >> B[i] >> T[i];
  
  cout << travelTime(n, m, l, A, B, T) << "\n";
}
#endif

Compilation message (stderr)

dreaming.cpp: In function 'int travelTime(int, int, int, int*, int*, int*)':
dreaming.cpp:51:15: warning: control reaches end of non-void function [-Wreturn-type]
   51 |   vector<int> ed;
      |               ^~

• Subtask 1: 0 / 14
• Subtask 2: 0 / 10
• Subtask 3: 0 / 23
• Subtask 4: 18 / 18
• Subtask 5: 0 / 12
• Subtask 6: 0 / 23