Submission #555631

#	Time	Username	Problem	Language	Result	Execution time	Memory
555631		iancu	Towns (IOI15_towns)	C++14	13 / 100	17 ms	1056 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 (cnt2 > 0 && dr + cnt1 > N / 2)
        leaves2.clear(), ok2 = false;
      if (cnt1 > 0 && st + cnt2 > N / 2)
        leaves1.clear(), ok1 = 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:6:32: warning: unused parameter 'sub' [-Wunused-parameter]
    6 |     int hubDistance(int N, int sub) {
      |                            ~~~~^~~
towns.cpp:9:19: warning: 'D1' may be used uninitialized in this function [-Wmaybe-uninitialized]
    9 |         if (dist[a][b] == -1)
      |                   ^
towns.cpp:10:48: 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