Submission #747226

#	Time	Username	Problem	Language	Result	Execution time	Memory
747226		math_rabbit_1028	Thousands Islands (IOI22_islands)	C++17	38.25 / 100	305 ms	26524 KiB

islands

#include "islands.h"
 
#include <bits/stdc++.h>
using namespace std;
 
bool ans = false;
vector<int> res;
 
int n, m;
vector< pair<int, int> > adj[101010], rev[101010];
int out[101010], in[101010], remain[202020];
 
set< pair<int, int> > outset;
 
int ch[202020];
vector<int> path1, path2, cycle, path3;
int junc;
void DFS(int v) {
  int cnt = 0;
  for (int i = 0; i < adj[v].size(); i++) {
    if (remain[adj[v][i].second] == 0) continue;
    if (ch[adj[v][i].first] == 0) {
      cnt++;
    }
  }
  if (cnt >= 2) {
    ans = true;
    junc = v;
    return;
  }
  for (int i = 0; i < adj[v].size(); i++) {
    if (remain[adj[v][i].second] == 0) continue;
    if (ch[adj[v][i].first] == 0) {
      ch[adj[v][i].first] = 1;
      path1.push_back(adj[v][i].second);
      DFS(adj[v][i].first);
    }
  }
}

int st = -1;
void path(int v) { 
  for (int i = 0; i < adj[v].size(); i++) {
    if (remain[adj[v][i].second] == 0) continue;
    if (ch[adj[v][i].first] == 0) {
      ch[adj[v][i].first] = 1;
      path2.push_back(adj[v][i].second);
      path(adj[v][i].first);
      if (st >= 0) return;
    }
    else {
      path2.push_back(adj[v][i].second);
      st = adj[v][i].first;
      return;
    }
  }
  path2.pop_back();
}

bool isconnect = false;
int iscycle[101010];
void check(int v) {
  if (iscycle[v] == 1) {
    st = v;
    isconnect = true;
    return;
  }
  for (int i = 0; i < adj[v].size(); i++) {
    if (remain[adj[v][i].second] == 0) continue;
    if (ch[adj[v][i].first] == 0) {
      ch[adj[v][i].first] = 1;
      path3.push_back(adj[v][i].second);
      check(adj[v][i].first);
    }
  }
  if (isconnect) return;
  path3.pop_back();
}

std::variant<bool, std::vector<int>> find_journey(
    int N, int M, std::vector<int> U, std::vector<int> V) {
  n = N; m = M;
  for (int i = 0; i < m; i++) {
    adj[U[i]].push_back({V[i], i});
    rev[V[i]].push_back({U[i], i});
    out[U[i]]++;
    in[V[i]]++;
    remain[i] = 1;
  }
 
  for (int i = 0; i < n; i++) outset.insert({out[i], i});
  while (!outset.empty() && outset.begin()->first == 0) {
    int v = outset.begin()->second;
    outset.erase(outset.begin());
    for (int i = 0; i < rev[v].size(); i++) {
      if (remain[rev[v][i].second] == 0) continue;
      remain[rev[v][i].second] = 0;
      outset.erase(outset.find(make_pair(out[rev[v][i].first], rev[v][i].first)));
      out[rev[v][i].first]--;
      outset.insert(make_pair(out[rev[v][i].first], rev[v][i].first));
    }
  }

  if (out[0] <= 1) {
    for (int i = 0; i < rev[0].size(); i++) {
      if (remain[rev[0][i].second] == 0) continue;
      remain[rev[0][i].second] = 0;
      outset.erase(outset.find(make_pair(out[rev[0][i].first], rev[0][i].first)));
      out[rev[0][i].first]--;
      outset.insert(make_pair(out[rev[0][i].first], rev[0][i].first));
    }
  }
  
  while (!outset.empty() && outset.begin()->first == 0) {
    int v = outset.begin()->second; 
    outset.erase(outset.begin());
    for (int i = 0; i < rev[v].size(); i++) {
      if (remain[rev[v][i].second] == 0) continue;
      remain[rev[v][i].second] = 0;
      outset.erase(outset.find(make_pair(out[rev[v][i].first], rev[v][i].first)));
      out[rev[v][i].first]--;
      outset.insert(make_pair(out[rev[v][i].first], rev[v][i].first));
    }
  }

  //for (int i = 0; i < m; i++) cout << remain[i] << "\n";
  //cout << "\n";
 
  ch[0] = 1;
  DFS(0);
  //for (int i = 0; i < n; i++) cout << ch[i] << " ";
  //cout << "\n";

  if (ans) {
    int idx = 0;
    for (int i = 0; i < path1.size(); i++) res.push_back(path1[i]);
    while (ch[adj[junc][idx].first] == 1) idx++;
    int first = adj[junc][idx].first;
    ch[first] = 1;
    path2.push_back(adj[junc][idx].second);
    path(first);

    int rev = -1, v = junc;
    for (int i = 0; i < path2.size(); i++) {
      if (v == st) {
        rev = i;
        break;
      }
      v = V[path2[i]];
    }
    for (int i = rev; i < path2.size(); i++) {
      cycle.push_back(path2[i]);
      iscycle[V[path2[i]]] = 1;
    }
    for (int i = 0; i < cycle.size(); i++) path2.pop_back();
    for (int i = 0; i < path2.size(); i++) res.push_back(path2[i]);
    for (int i = 0; i < cycle.size(); i++) res.push_back(cycle[i]);
    for (int i = path2.size() - 1; i >= 0; i--) res.push_back(path2[i]);

    //for (int i = 0; i < n; i++) cout << ch[i] << " ";
    //cout << "\n";
    //for (int i = 0; i < n; i++) cout << iscycle[i] << " ";
    //cout << "\n";

    for (int i = 0; i < n; i++) ch[i] = 0;
    st = -1;
    path1.clear();
    ch[0] = 1;
    DFS(0);

    idx++;
    while (ch[adj[junc][idx].first] == 1) idx++;
    int second = adj[junc][idx].first;
    ch[second] = 1;
    path3.push_back(adj[junc][idx].second);
    check(second);
    if (isconnect) {
      for (int i = 0; i < path3.size(); i++) res.push_back(path3[i]);
      int k = 0;
      for (int i = 0; i < cycle.size(); i++) if (V[cycle[i]] == st) k = i;
      for (int i = k; i >= 0; i--) res.push_back(cycle[i]);
      for (int i = cycle.size() - 1; i > k; i--) res.push_back(cycle[i]);
      for (int i = path3.size() - 1; i >= 0; i--) res.push_back(path3[i]);
    }
    else {
      //cout << "!!!";
    }
    for (int i = path1.size() - 1; i >= 0; i--) res.push_back(path1[i]);
    return res;
  }
  else return ans;
}

Compilation message (stderr)

islands.cpp: In function 'void DFS(int)':
islands.cpp:20:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |   for (int i = 0; i < adj[v].size(); i++) {
      |                   ~~^~~~~~~~~~~~~~~
islands.cpp:31:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |   for (int i = 0; i < adj[v].size(); i++) {
      |                   ~~^~~~~~~~~~~~~~~
islands.cpp: In function 'void path(int)':
islands.cpp:43:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |   for (int i = 0; i < adj[v].size(); i++) {
      |                   ~~^~~~~~~~~~~~~~~
islands.cpp: In function 'void check(int)':
islands.cpp:68:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   68 |   for (int i = 0; i < adj[v].size(); i++) {
      |                   ~~^~~~~~~~~~~~~~~
islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:95:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   95 |     for (int i = 0; i < rev[v].size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~
islands.cpp:105:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  105 |     for (int i = 0; i < rev[0].size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~
islands.cpp:117:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  117 |     for (int i = 0; i < rev[v].size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~
islands.cpp:136:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  136 |     for (int i = 0; i < path1.size(); i++) res.push_back(path1[i]);
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:144:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  144 |     for (int i = 0; i < path2.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:151:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  151 |     for (int i = rev; i < path2.size(); i++) {
      |                       ~~^~~~~~~~~~~~~~
islands.cpp:155:23: 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 < cycle.size(); i++) path2.pop_back();
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:156:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  156 |     for (int i = 0; i < path2.size(); i++) res.push_back(path2[i]);
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:157:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  157 |     for (int i = 0; i < cycle.size(); i++) res.push_back(cycle[i]);
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:178:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  178 |       for (int i = 0; i < path3.size(); i++) res.push_back(path3[i]);
      |                       ~~^~~~~~~~~~~~~~
islands.cpp:180:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  180 |       for (int i = 0; i < cycle.size(); i++) if (V[cycle[i]] == st) k = i;
      |                       ~~^~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 15.749999999999998 / 45