Submission #1058166

#	Time	Username	Problem	Language	Result	Execution time	Memory
1058166		SalihSahin	Thousands Islands (IOI22_islands)	C++17	10 / 100	16 ms	4472 KiB

islands

#include<bits/stdc++.h>
#define pb push_back
using namespace std;
#include "islands.h"

const int N = 1e3 + 5;

vector<int> nodes, cycle, adj[N];
vector<bool> vis(N);

void dfs(int node){
    if(cycle.size() > 0) return;
    nodes.pb(node);
    vis[node] = 1;

    for(auto itr: adj[node]){
        if(!vis[itr]){
            dfs(itr);
        }
        if(itr == 0 && nodes.size() > 2) cycle = nodes;
        if(cycle.size() > 0) return;
    }

    nodes.pop_back();
}

std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
  if(N == 2){ // subtask 1
    vector<int> c[2];
    for(int i = 0; i < M; i++){
        if(U[i] == 0) c[0].pb(i);
        else c[1].pb(i);
    }

    if(c[0].size() > 1 && c[1].size() > 0){
        int x = c[0][0], y = c[0][1], z = c[1][0];
        vector<int> ans = {x, z, y, x, z, y};
        return ans;
    }
    else return false;
  }

  if(N <= 400){ // subtask 2
    vector<vector<int> > cnt(N, vector<int>(N, -1));
    for(int i = 0; i < M; i++){
        cnt[U[i]][V[i]] = i;
    }
    bool ok = 1;

    for(int i = 0; i < N; i++){
        for(int j = 0; j < N; j++){
            if(i == j) continue;
            if(cnt[i][j] == -1) ok = 0;
        }
    }

    if(ok){
        int c0 = cnt[0][1];
        int c1 = cnt[1][2];
        int c2 = cnt[2][0];

        int c3 = cnt[0][2];
        int c4 = cnt[2][1];
        int c5 = cnt[1][0];

        vector<int> ans = {c0, c1, c2, c3, c4, c5, c2, c1, c0, c5, c4, c3};
        return ans;
    }
  }

  bool subtask3 = 1;

  vector<vector<int> > num(N, vector<int>(N));
  for(int i = 0; i < M; i++){
     adj[U[i]].pb(V[i]);
     num[U[i]][V[i]] = i;

     if(i % 2 == 0 && (U[i] != V[i+1] || V[i] != U[i+1])){
        subtask3 = 0;
     }
  }

  if(subtask3){
     dfs(0);
     if(!cycle.size()){
        return false;
     }
     else{
        vector<int> c1, c2;
        for(int i = 0; i < cycle.size(); i++){
            c1.pb(num[cycle[i]][cycle[(i + 1) % cycle.size()]]);
        }
        for(int i = cycle.size()-1; i >= 0; i--){
            c2.pb(num[cycle[(i + 1) % cycle.size()]][cycle[i]]);
        }

        vector<int> ans;
        for(auto itr: c1){
            ans.pb(itr);
        }
        for(auto itr: c2){
            ans.pb(itr);
        }
        reverse(c1.begin(), c1.end());
        reverse(c2.begin(), c2.end());
        for(auto itr: c1){
            ans.pb(itr);
        }
        for(auto itr: c2){
            ans.pb(itr);
        }

        return ans;
     }
  }


  return false;
}
/*
int main() {
  int N, M;
  assert(2 == scanf("%d %d", &N, &M));

  std::vector<int> U(M), V(M);
  for (int i = 0; i < M; ++i) {
    assert(2 == scanf("%d %d", &U[i], &V[i]));
  }

  std::variant<bool, std::vector<int>> result = find_journey(N, M, U, V);
  if (result.index() == 0) {
    printf("0\n");
    if (std::get<bool>(result)) {
      printf("1\n");
    } else {
      printf("0\n");
    }
  } else {
    printf("1\n");
    std::vector<int> &canoes = std::get<std::vector<int>>(result);
    printf("%d\n", static_cast<int>(canoes.size()));
    for (int i = 0; i < static_cast<int>(canoes.size()); ++i) {
      if (i > 0) {
        printf(" ");
      }
      printf("%d", canoes[i]);
    }
    printf("\n");
  }
  return 0;
}
*/

Compilation message (stderr)

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:90:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   90 |         for(int i = 0; i < cycle.size(); i++){
      |                        ~~^~~~~~~~~~~~~~

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