Submission #1034659

#	Time	Username	Problem	Language	Result	Execution time	Memory
1034659		Mr_Husanboy	Thousands Islands (IOI22_islands)	C++17	8.40 / 100	22 ms	6484 KiB

islands

#include "islands.h"

#include <variant>
#include <bits/stdc++.h>

using namespace std;

#define ff first
#define ss second
#define all(a) (a).begin(), (a).end()
#define ll long long
const int mod = 1000002022;

vector<int> state, p;
int n, m; 
vector<vector<int>> g;
template<typename T>
int len(T &a){return a.size();}

mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());


variant<bool, vector<int>> find_journey(
    int n, int m, std::vector<int> u, std::vector<int> v) {
  vector<vector<int>> g(n);
  for(int i = 0; i < m; i ++) g[u[i]].push_back(i);
  if(len(g[0]) == 0) return false;

  vector<int> ans;
  vector<int> vis(n);
  vector<int> cyc;
  vector<int> par(n);
  auto dfs = [&](auto &dfs, int i)->bool{
    vis[i] = 1;
    int r = 0;
    for(auto j : g[i]){
      if(j % 2) continue;
      int x = v[j];
      par[x] = j;
      if(vis[x] == 2) continue;
      if(vis[x] == 1){
        cyc.push_back(j);
        int cur = i;
        while(cur != x){
          cyc.push_back(par[cur]);
          cur = u[par[cur]];
        }
        return true;
      }
      if(dfs(dfs, x)){
        return true;
      }
    }
    vis[i] = 2;
    return false;
  };

  if(!dfs(dfs, 0)){
    return false;
  }
  int j = u[cyc.back()];

  // while(j != 0){
  //   ans.push_back(par[j]);
  //   j = u[par[j]];
  // }
  reverse(all(ans));
  reverse(all(cyc));

  vector<int> res;
  for(auto i : ans) res.push_back(i);
  for(auto i : cyc) res.push_back(i);
  for(auto i : cyc) res.push_back(i ^ 1);
  reverse(all(cyc));
  for(auto i : cyc) res.push_back(i);
  for(auto i : cyc) res.push_back(i ^ 1);

  reverse(all(ans));
  for(auto i : ans) res.push_back(i ^ 1);
  return res;
}

Compilation message (stderr)

islands.cpp: In instantiation of 'find_journey(int, int, std::vector<int>, std::vector<int>)::<lambda(auto:23&, int)> [with auto:23 = find_journey(int, int, std::vector<int>, std::vector<int>)::<lambda(auto:23&, int)>]':
islands.cpp:58:10:   required from here
islands.cpp:35:9: warning: unused variable 'r' [-Wunused-variable]
   35 |     int r = 0;
      |         ^
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:61:7: warning: unused variable 'j' [-Wunused-variable]
   61 |   int j = u[cyc.back()];
      |       ^

• Subtask 1: 0 / 5
• Subtask 2: 0 / 5
• Subtask 3: 0 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 0 / 45