Submission #553107

#	Time	Username	Problem	Language	Result	Execution time	Memory
553107		iancu	Towns (IOI15_towns)	C++14	13 / 100	23 ms	872 KiB

towns

#include "towns.h"
#include <vector>

using namespace std;

int hubDistance(int N, int sub) {
  vector<vector<int>> dist(N, vector<int>(N, -1));
  auto getDist = [&dist](int a, int b) {
    if (dist[a][b] == -1)
      dist[a][b] = dist[b][a] = getDistance(a, b);
    return dist[a][b];
  };
  int D1, D2, dist_max = 0;
  for (int i = 1; i < N; ++i)
    if (getDist(0, i) > dist_max) {
      dist_max = getDist(0, i);
      D1 = i;
    }
  dist_max = 0;
  for (int i = 0; i < N; ++i)
    if (i != D1 && getDist(D1, i) > dist_max) {
      dist_max = getDist(D1, i);
      D2 = i;
    }
  int R = getDist(D1, D2);
  for (int i = 0; i < N; ++i)
    if (i != D1 && i != 0) {
      int dist_i = (getDist(i, D1) - getDist(i, 0) + getDist(D1, 0)) / 2;
      R = min(R, max(dist_i, getDist(D1, D2) - dist_i));
    }
  vector<int> leaves1, leaves2;
  int cnt1 = 0, cnt2 = 0;
  int st = 0, dr = 0;
  for (int i = 0; i < N; ++i)
    if (i != D1 && i != 0) {
      int dist_i = (getDist(i, D1) - getDist(i, 0) + getDist(D1, 0)) / 2;
      if (R == max(dist_i, getDist(D1, D2) - dist_i)) {
        if (R == dist_i) {
          ++cnt1;
          leaves1.push_back(i);
        } else {
          ++cnt2;
          leaves2.push_back(i);
        }
      } else if (dist_i < getDist(D1, D2) - dist_i) {
        ++st;
      } else {
        ++dr;
      }
    }
  if (st > N / 2 || dr > N / 2)
    return -R;
  bool ok1 = true, ok2 = true;
  if (cnt1 > 0 && dr + cnt2 > N / 2)
    leaves1.clear(), ok1 = false;
  if (cnt2 > 0 && st + cnt1 > N / 2)
    leaves2.clear(), ok2 = false;
  if (!ok1 && !ok2)
    return -R;
  auto sameSubtree = [&dist, &D1, &D2, &getDist](int a, int b, int _R) {
    int dist_lca = (getDist(a, D1) + getDist(b, D1) - getDist(a, b)) / 2;
    if (dist_lca <= _R)
      return false;
    return true;
  };
  int candidat, ap = 0;
  for (auto i: leaves1)
    if (ap == 0) {
      candidat = i;
      ap = 1;
    } else {
      if (sameSubtree(i, candidat, R))
        ++ap;
      else
        --ap;
    }
  ap = 0;
  for (auto i: leaves1)
    if (sameSubtree(i, candidat, R))
      ++ap;
  if (ap > N / 2)
    ok1 = false;
  //////
  ap = 0;
  for (auto i: leaves2)
    if (ap == 0) {
      candidat = i;
      ap = 1;
    } else {
      if (sameSubtree(i, candidat, getDist(D1, D2) - R))
        ++ap;
      else
        --ap;
    }
  ap = 0;
  for (auto i: leaves2)
    if (sameSubtree(i, candidat, getDist(D1, D2) - R))
      ++ap;
  if (ap > N / 2)
    ok2 = false;
  if (ok1 || ok2)
    return R;
  return -R;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:6:28: warning: unused parameter 'sub' [-Wunused-parameter]
    6 | int hubDistance(int N, int sub) {
      |                        ~~~~^~~
towns.cpp:9:15: warning: 'D1' may be used uninitialized in this function [-Wmaybe-uninitialized]
    9 |     if (dist[a][b] == -1)
      |               ^
towns.cpp:10:44: warning: 'D2' may be used uninitialized in this function [-Wmaybe-uninitialized]
   10 |       dist[a][b] = dist[b][a] = getDistance(a, b);
      |                                 ~~~~~~~~~~~^~~~~~

• Subtask 1: 13 / 13
• Subtask 2: 0 / 12
• Subtask 3: 0 / 13
• Subtask 4: 0 / 10
• Subtask 5: 0 / 13
• Subtask 6: 0 / 39