Submission #557648

#	Time	Username	Problem	Language	Result	Execution time	Memory
557648		iancu	Towns (IOI15_towns)	C++14	100 / 100	25 ms	816 KiB

towns

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

using namespace std;

class DSU {
private:
  vector<int> par;
  map<int, int> poz;
public:
  DSU(const vector<int>& v) {
    for (int i = 0; i < v.size(); ++i)
      poz[v[i]] = i;
    for (int i = 0; i < v.size(); ++i)
      par.push_back(i);
  }
  int getRoot(int x) {
    if (x == par[x])
      return x;
    return par[x] = getRoot(par[x]);
  }
  bool query(int a, int b) {
    a = poz[a], b = poz[b];
    int ra = getRoot(a);
    int rb = getRoot(b);
    return ra == rb;
  }
  void join(int a, int b) {
    a = poz[a], b = poz[b];
    int ra = getRoot(a);
    int rb = getRoot(b);
    par[ra] = rb;
  }
  bool isRoot(int x) {
    x = poz[x];
    return x == getRoot(x);
  }
  int getSize(int x) {
    x = getRoot(poz[x]);
    int sz = 0;
    for (int i = 0; i < par.size(); ++i)
      sz += (getRoot(i) == x);
    return sz;
  }
};

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) {
      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;
  int R_init = R;
  vector<int> leaves;
  if (leaves1.size() > leaves2.size()) {
    leaves = leaves1;
  } else {
    leaves = leaves2;
    R = getDist(D1, D2) - R;
  }
  auto sameSubtree = [&dist, &D1, &D2, &getDist, &R](int a, int b) {
    int dist_lca = (getDist(a, D1) + getDist(b, D1) - getDist(a, b)) / 2;
    if (dist_lca <= R)
      return false;
    return true;
  };
  if (leaves.empty())
    return R_init;
  DSU dsu(leaves);
  vector<int> cand = leaves;
  int fin = leaves.back();
  while (!cand.empty()) {
    vector<int> new_cand;
    for (int i = 0; i < cand.size(); i += 2) {
      if (i < cand.size() - 1) {
        if (sameSubtree(cand[i], cand[i + 1])) {
          dsu.join(cand[i], cand[i + 1]);
          new_cand.push_back(cand[i]);
        }
      } else {
        fin = cand[i];
      }
    }
    cand = new_cand;
  }
  int ap = 0;
  for (auto i: leaves)
    if (dsu.isRoot(i) && sameSubtree(fin, i))
      ap += dsu.getSize(i);
  if (ap > N / 2)
    return -R_init;
  return R_init;
}

Compilation message (stderr)

towns.cpp: In constructor 'DSU::DSU(const std::vector<int>&)':
towns.cpp:13:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |     for (int i = 0; i < v.size(); ++i)
      |                     ~~^~~~~~~~~~
towns.cpp:15:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |     for (int i = 0; i < v.size(); ++i)
      |                     ~~^~~~~~~~~~
towns.cpp: In member function 'int DSU::getSize(int)':
towns.cpp:42:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |     for (int i = 0; i < par.size(); ++i)
      |                     ~~^~~~~~~~~~~~
towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:115:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  115 |     for (int i = 0; i < cand.size(); i += 2) {
      |                     ~~^~~~~~~~~~~~~
towns.cpp:116:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  116 |       if (i < cand.size() - 1) {
      |           ~~^~~~~~~~~~~~~~~~~
towns.cpp:48:28: warning: unused parameter 'sub' [-Wunused-parameter]
   48 | int hubDistance(int N, int sub) {
      |                        ~~~~^~~
towns.cpp:51:15: warning: 'D1' may be used uninitialized in this function [-Wmaybe-uninitialized]
   51 |     if (dist[a][b] == -1)
      |               ^
towns.cpp:52:44: warning: 'D2' may be used uninitialized in this function [-Wmaybe-uninitialized]
   52 |       dist[a][b] = dist[b][a] = getDistance(a, b);
      |                                 ~~~~~~~~~~~^~~~~~

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