Submission #632250

#	Time	Username	Problem	Language	Result	Execution time	Memory
632250		Minindu2006	Thousands Islands (IOI22_islands)	C++17	55 / 100	42 ms	6344 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
#include <variant>
#include <vector>
using namespace std;
int n, m, can = 0;
vector<int> u, v, vis, adjj[1001];
vector<pair<int, int>> adj[1001];
void dfs(int node, vector<int> &ans)
{
  vis[node] = 1;
  if (node == 0)
  {
    if (adj[node].size() >= 2)
    {
      can = 1;
      vector<int> cur(4);
      for (int i = 0; i < 2; i++)
      {
        int bNum = adj[node][i].second;
        cur[2 * i] = bNum;
        cur[2 * i + 1] = (bNum % 2 == 1 ? bNum - 1 : bNum + 1);
        ans.push_back(cur[2 * i]);
        ans.push_back(cur[2 * i + 1]);
      }
      ans.push_back(cur[1]);
      ans.push_back(cur[0]);
      ans.push_back(cur[3]);
      ans.push_back(cur[2]);
      return;
    }
  }
  else
  {
    if (adj[node].size() >= 3)
    {

      can = 1;
      int i = 0, lboat1 = ans.back(), lboat2 = (lboat1 % 2 == 1 ? lboat1 - 1 : lboat1 + 1), sz = ans.size();
      ;
      vector<int> cur(4);
      for (auto k : adj[node])
      {
        if (i == 2)
          break;
        if (k.second == lboat2)
          continue;
        int bNum = k.second;
        cur[2 * i] = bNum;
        cur[2 * i + 1] = (bNum % 2 == 1 ? bNum - 1 : bNum + 1);
        ans.push_back(cur[2 * i]);
        ans.push_back(cur[2 * i + 1]);
        i++;
      }
      ans.push_back(cur[1]);
      ans.push_back(cur[0]);
      ans.push_back(cur[3]);
      ans.push_back(cur[2]);
      for (int i = sz - 1; i >= 0; i--)
        ans.push_back(ans[i]);
      return;
    }
  }
  for (auto a : adj[node])
  {
    if (vis[a.first])
      continue;
    ans.push_back(a.second);
    dfs(a.first, ans);
    if (can == 1)
      return;
    ans.pop_back();
  }
}

vector<int> col, par, cycc, sts;
int cs, ce;
int cycle(int node)
{
  col[node] = 1;
  for (auto k : adjj[node])
  {
    if (col[k] == 0)
    {
      par[k] = node;
      if (cycle(k))
        return 1;
    }
    else if (col[k] == 1)
    {
      ce = node;
      cs = k;
      return 1;
    }
  }
  col[node] = 2;
  return 0;
}

variant<bool, std::vector<int>> sb4()
{
  col.resize(n, 0);
  par.resize(n, -1);
  for (int i = 0; i < m; i += 2)
    adjj[u[i]].push_back(v[i]);
  int cyc = cycle(0);
  if (cyc == 0)
    return false;
  cycc.push_back(cs);
  int nod2 = ce;
  while (nod2 != cs)
  {
    cycc.push_back(nod2);
    nod2 = par[nod2];
  }
  cycc.push_back(cs);
  sts.push_back(cs);
  while (nod2 != -1)
  {
    sts.push_back(nod2);
    nod2 = par[nod2];
  }
  reverse(cycc.begin(), cycc.end());
  reverse(sts.begin(), sts.end());

  if (cycc[0] == 0)
  {
    vector<int> mid;
    int extra;
    for (int i = 0; i < cycc.size() - 1; i++)
    {
      for (int j = 0; j < m; j += 2)
      {
        if (u[j] == cycc[i] && v[j] == cycc[i + 1])
        {
          mid.push_back(j);
          if(i == 0)
            extra = j + 1;
          break;
        }
      }
    }
    vector<int> ans;
    ans.insert(ans.end(), mid.begin(), mid.end());
    ans.push_back(extra);
    reverse(mid.begin(), mid.end());
    ans.push_back(mid.back());
    mid.pop_back();
    mid.push_back(extra);
    ans.insert(ans.end(), mid.begin(), mid.end());
    return ans;
  }

  vector<int> fst, lst, mid;
  for (int i = 0; i < sts.size() - 1; i++)
  {
    for (int j = 0; j < m; j += 2)
    {
      if (u[j] == sts[i] && v[j] == sts[i + 1])
      {
        fst.push_back(j);
        lst.push_back(j + 1);
        break;
      }
    }
  }
  for (int i = 0; i < cycc.size() - 1; i++)
  {
    for (int j = 0; j < m; j += 2)
    {
      if (u[j] == cycc[i] && v[j] == cycc[i + 1])
      {
        mid.push_back(j);
        break;
      }
    }
  }

  vector<int> ans;
  // fst half
  ans.insert(ans.end(), fst.begin(), fst.end());
  ans.insert(ans.end(), mid.begin(), mid.end());
  reverse(fst.begin(), fst.end());
  reverse(mid.begin(), mid.end());
  ans.insert(ans.end(), fst.begin(), fst.end());

  // sec half
  ans.insert(ans.end(), lst.begin(), lst.end());
  ans.insert(ans.end(), mid.begin(), mid.end());
  reverse(lst.begin(), lst.end());
  ans.insert(ans.end(), lst.begin(), lst.end());
  return ans;
}
variant<bool, std::vector<int>> sb3()
{
  vector<int> ans;
  vis.resize(n, 0);
  for(int i=0;i<m;i+=2)
  {
    adj[u[i]].push_back({v[i], i});
    adj[v[i]].push_back({u[i], i + 1});
  }
  dfs(0, ans);
  if(can)
    return ans;
  return false;
}
variant<bool, std::vector<int>> sb2()
{
  int a, b, c, d;
  for(int i=0;i<m;i++)
  {
    if(u[i] == 0 && v[i] == 1)
      a = i;
    if(u[i] == 1 && v[i] == 0)
      b = i;
    if(u[i] == 0 && v[i] == 2)
      c = i;
    if(u[i] == 2 && v[i] == 0)
      d = i;
  }
  return vector<int> ({a, b, c, d, b, a, d, c});
}
variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V)
{
  n = N, m = M;
  u = U, v = V;

  vector<int> ans;
  if (n <= 2)
  {
    if (m <= 2)
      return false;
    int z = 0;
    vector<int> cur(3);
    for (int i = 0; i < m; i++)
    {
      if (u[i] == 0)
      {
        if (z < 2)
          cur[z] = i;
        z++;
      }
      else
        cur[2] = i;
    }
    if (z < 2 || z == m)
      return false;
    ans.resize(3);
    ans[0] = cur[0];
    ans[1] = cur[2];
    ans[2] = cur[1];
    for (int i = 0; i < 3; i++)
      ans.push_back(ans[i]);
    return ans;
  }
  int sb31 = 1, sb41 = 1;
  for(int i=0;i<m;i+=2)
  {
    sb31 = sb31 & ((u[i] == v[i + 1]) & (v[i] == u[i + 1]));
    sb41 = sb41 & ((u[i] == u[i + 1]) & (v[i] == v[i + 1]));
  }
  if(sb31)
    return sb3();
  if(sb41)
    return sb4();
  return sb2();
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > sb4()':
islands.cpp:130:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  130 |     for (int i = 0; i < cycc.size() - 1; i++)
      |                     ~~^~~~~~~~~~~~~~~~~
islands.cpp:155:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  155 |   for (int i = 0; i < sts.size() - 1; i++)
      |                   ~~^~~~~~~~~~~~~~~~
islands.cpp:167:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  167 |   for (int i = 0; i < cycc.size() - 1; i++)
      |                   ~~^~~~~~~~~~~~~~~~~
islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > sb2()':
islands.cpp:222:47: warning: 'd' may be used uninitialized in this function [-Wmaybe-uninitialized]
  222 |   return vector<int> ({a, b, c, d, b, a, d, c});
      |                                               ^
islands.cpp:222:47: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:222:47: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:222:47: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 21 / 21
• Subtask 4: 24 / 24
• Subtask 5: 0 / 45