Submission #683196

#	Time	Username	Problem	Language	Result	Execution time	Memory
683196		MilosMilutinovic	Towns (IOI15_towns)	C++14	13 / 100	14 ms	400 KiB

towns

#include "towns.h"
#include <bits/stdc++.h>

using namespace std;

int hubDistance(int n, int sub) {
  vector<vector<int>> w(n, vector<int>(n, -1));
  for (int i = 0; i < n; i++) {
    w[i][i] = 0;
  }
  auto Ask = [&](int i, int j) {
    if (w[i][j] == -1) {
      int d = getDistance(i, j);
      w[i][j] = w[j][i] = d;
    }
    return w[i][j];
  };
  int v, u;
  {
    vector<int> dist(n);
    for (int i = 1; i < n; i++) {
      dist[i] = Ask(0, i);
    }
    v = max_element(dist.begin(), dist.end()) - dist.begin();
  }
  {
    vector<int> dist(n);
    for (int i = 0; i < n; i++) {
      dist[i] = Ask(i, v);
    }
    u = max_element(dist.begin(), dist.end()) - dist.begin();
  }
  int diam = Ask(v, u);
  int res = diam;
  vector<int> f;
  vector<int> d(n);
  vector<int> e(n);
  for (int i = 0; i < n; i++) {
    if (u == i || v == i) {
      continue;
    }
    int d_vi = Ask(v, i);
    int d_ui = Ask(u, i);
    int diff = d_vi - d_ui;
    // dv + du = diam
    // dv - du = diff
    int dv = (diam + diff) / 2;
    int du = diam - dv;
    d[i] = d_vi - dv;
    e[i] = dv;
    res = min(res, max(dv, du));
    f.push_back(dv);
  }
  sort(f.begin(), f.end());
  vector<int> ch;
  for (int i = 0; i < (int) f.size(); i++) {
    if (i == 0 || f[i] != f[i - 1]) {
      ch.push_back(1);
    } else {
      ch.back() += 1;
    }
  }
  f.erase(unique(f.begin(), f.end()), f.end());
  assert(is_sorted(f.begin(), f.end()));
  int m = (int) f.size();
  {
    int L = 1, R = n - 1;
    for (int i = 0; i < m; i++) {
      R -= ch[i];
      if (res == max(f[i], diam - f[i])) {
        if (L <= n / 2 && R <= n / 2 && ch[i] <= n / 2) {
          return res;
        }
      }
      L += ch[i];
    }
  }
  auto Connected = [&](int x, int y) {
    int d_xy = Ask(x, y);
    return d_xy < d[x] + d[y];
  };
  auto Solve = [&](int r) {
    vector<int> ver;
    for (int i = 0; i < n; i++) {
      if (i != u && i != v && e[i] == f[r]) {
        ver.push_back(i);
      }
    }
    if ((int) ver.size() <= n / 2) {
      return true;
    }
    int maj = -1;
    int bal = 0;
    for (int i : ver) {
      if (bal == 0) {
        maj = i;
        bal = 1;
      } else {
        if (Connected(maj, i)) {
          bal++;
        } else {
          bal--;
        }
      }
    }
    int cnt = 0;
    vector<int> seen;
    vector<bool> in(n);
    for (int i : ver) {
      bool found = false;
      bool ok = false;
      for (int x : seen) {
        if (w[x][i] != -1) {
          found = true;
          if (in[x] && Connected(x, i)) {
            ok = true;
          }
        }
      }
      if (!found) {
        if (Connected(maj, i)) {
          in[i] = true;
          cnt += 1;
        }
      } else {
        if (ok) {
          in[i] = true;
          cnt += 1;
        }
      }
      seen.push_back(i);
    }
    return cnt <= n / 2;
  };
  int L = 1, R = n - 1, med = 0;
  for (int i = 0; i < m; i++) {
    R -= ch[i];
    if (res == max(f[i], diam - f[i])) {
      if (L <= n / 2 && R <= n / 2 && Solve(i)) {
        //med++;
        //assert(med <= 2);
        return res;
      }
    }
    L += ch[i];
  }
  return -res;
}

/*
1 1
11
0 17 18 20 17 12 20 16 23 20 11
17 0 23 25 22 17 25 21 28 25 16
18 23 0 12 21 16 24 20 27 24 17
20 25 12 0 23 18 26 22 29 26 19
17 22 21 23 0 9 21 17 26 23 16
12 17 16 18 9 0 16 12 21 18 11
20 25 24 26 21 16 0 10 29 26 19
16 21 20 22 17 12 10 0 25 22 15
23 28 27 29 26 21 29 25 0 21 22
20 25 24 26 23 18 26 22 21 0 19
11 16 17 19 16 11 19 15 22 19 0

17
*/

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:24:47: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   24 |     v = max_element(dist.begin(), dist.end()) - dist.begin();
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:31:47: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   31 |     u = max_element(dist.begin(), dist.end()) - dist.begin();
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:135:25: warning: unused variable 'med' [-Wunused-variable]
  135 |   int L = 1, R = n - 1, med = 0;
      |                         ^~~
towns.cpp:6:28: warning: unused parameter 'sub' [-Wunused-parameter]
    6 | int hubDistance(int n, int sub) {
      |                        ~~~~^~~

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