Submission #787589

#	Time	Username	Problem	Language	Result	Execution time	Memory
787589		thimote75	Thousands Islands (IOI22_islands)	C++17	35 / 100	157 ms	38060 KiB

islands

#include "islands.h"

#include <bits/stdc++.h>

using namespace std;

using idata = vector<int>;
using igrid = vector<idata>;
using graph = vector<vector<pair<pair<int, bool>, int>>>;
using bdata = vector<bool>;
using bgrid = vector<bdata>;

graph roads;

bgrid visited;
bgrid visiting;
bdata used;
idata path;

bool dfs (int node, int type, int last) {
  if (visited[node][type] && !visiting[node][type]) return false;
  if (visiting[node][type]) {
    if (type == 1) return true;
    type ++;
    if (visited[node][type]) return false;
  }

  visiting[node][type] = true;
  visited [node][type] = true;

  for (const auto &road : roads[node]) {
    int id   = road.first.first;
    int next = road.second;
    if (used[id] != road.first.second || last == id) continue ;

    used[id] = !road.first.second;
    if (dfs(next, type, id))
      return true;
    used[id] = road.first.second;
  }

  visiting[node][type] = false;
  return false;
}

std::variant<bool, idata> find_journey(
    int N, int M, idata U, idata V) {
  roads.resize(N);
  visited.resize(N, bdata(2)); visiting.resize(N, bdata(2));
  used.resize(M);
  bool st3 = M % 2 == 0;
  for (int i = 0; i < M; i ++) {
    roads[U[i]].push_back({ {i, false}, V[i] });
    roads[V[i]].push_back({ {i, true }, U[i] });
  }
  
  if (!dfs(0, 0, -1)) return false;

  return true;
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, idata, idata)':
islands.cpp:51:8: warning: unused variable 'st3' [-Wunused-variable]
   51 |   bool st3 = M % 2 == 0;
      |        ^~~

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