Submission #668384

#	Time	Username	Problem	Language	Result	Execution time	Memory
668384		600Mihnea	City Mapping (NOI18_citymapping)	C++17	100 / 100	20 ms	852 KiB

citymapping

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

using namespace std;

typedef long long ll;

map<pair<int, int>, ll> mp;

ll ask(int i, int j)
{
  if (i == j)
  {
    return 0;
  }
  if (i > j)
  {
    swap(i, j);
  }
  if (!mp.count({i, j}))
  {
    mp[{i, j}] = get_distance(i + 1, j + 1);
  }
  return mp[{i, j}];
}

void find_roads(int n, int q, int e_a[], int e_b[], int e_w[])
{
  int root = 0;
  vector<ll> dist0(n, 0);
  vector<int> ord;
  for (int i = 0; i < n; i++)
  {
    if (root == i)
    {
      dist0[i] = 0;
      continue;
    }
    dist0[i] = ask(root, i);
    ord.push_back(i);
  }
  sort(ord.begin(), ord.end(), [&] (int i, int j) {return dist0[i] < dist0[j];});
  vector<int> deja = {0};
  vector<vector<int>> g(n);
  vector<int> sub(n), big(n), u(n), par(n);
  int top = 0;

  auto add_edge = [&] (int a, int b)
  {
    e_a[top] = a + 1;
    e_b[top] = b + 1;
    e_w[top] = dist0[b] - dist0[a];
    g[a].push_back(b);
    top++;
  };

  function<void(int)> dfs = [&] (int a)
  {
    sub[a] = 1;
    if (g[a].empty())
    {
      u[a] = a;
      return;
    }
    big[a] = g[a][0];
    for (auto &b : g[a])
    {
      dfs(b);
      par[b] = a;
      sub[a] += sub[b];
      if (sub[b] > sub[big[a]])
      {
        big[a] = b;
      }
    }
    u[a] = u[big[a]];
  };

  function<void(int, int)> locate = [&] (int root, int new_vertex)
  {
    if (sub[root] == 1)
    {
      add_edge(root, new_vertex);
      return;
    }
    int b = u[root];
    ll dist_b_v = ask(b, new_vertex);
    ll dist_b_r = dist0[b] - dist0[root];
    ll dist_v_r = dist0[new_vertex] - dist0[root];
    ll sum_dub = (dist_b_v + dist_b_r + dist_v_r);
    ll sum = sum_dub / 2;
    ll z = sum - dist_b_r;
    ll x = sum - dist_b_v;
    ll y = sum - dist_v_r;
    int fix_inainte = -1;
    if (y == 0)
    {
      add_edge(b, new_vertex);
      return;
    }
    while (y > 0)
    {
      y -= (dist0[b] - dist0[par[b]]);
      fix_inainte = b;
      b = par[b];
    }
    int mid_point = b;
    if (z == 0)
    {
      add_edge(mid_point, new_vertex);
      return;
    }
    if ((int) g[mid_point].size() == 1)
    {
      add_edge(mid_point, new_vertex);
      return;
    }
    vector<int> oth;
    for (auto &vecin : g[mid_point])
    {
      if (vecin == fix_inainte)
      {
        continue;
      }
      oth.push_back(vecin);
    }
    if ((int) oth.size() == 1)
    {
      if (dist0[oth[0]] - dist0[mid_point] >= z)
      {
        add_edge(mid_point, new_vertex);
        return;
      }
      if (ask(u[oth[0]], new_vertex) == z + dist0[u[oth[0]]] - dist0[mid_point])
      {
        add_edge(mid_point, new_vertex);
        return;
      }
      locate(oth[0], new_vertex);
      return;
    }
    if (ask(oth[0], new_vertex) < ask(oth[1], new_vertex))
    {
      locate(oth[0], new_vertex);
    }
    else
    {
      locate(oth[1], new_vertex);
    }
  };

  for (auto &vertex : ord)
  {
    dfs(root);
    locate(root, vertex);
  }
}

Compilation message (stderr)

citymapping.cpp: In lambda function:
citymapping.cpp:93:8: warning: unused variable 'x' [-Wunused-variable]
   93 |     ll x = sum - dist_b_v;
      |        ^

• Subtask 1: 9 / 9
• Subtask 2: 16 / 16
• Subtask 3: 13 / 13
• Subtask 4: 19 / 19
• Subtask 5: 43 / 43