Submission #1149599

#	Time	Username	Problem	Language	Result	Execution time	Memory
1149599		byunjaewoo	Thousands Islands (IOI22_islands)	C++20	21 / 100	16 ms	3144 KiB

islands

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

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
  int a=-1, b=-1, c=-1, d=-1;
  for(int i=0; i<M; i+=2) {
    if(U[i]==0) {
      if(a<0) a=i, c=i+1;
      else if(b<0) b=i, d=i+1;
    }
    if(V[i]==0) {
      if(a<0) a=i+1, c=i;
      else if(b<0) b=i+1, d=i;
    }
  }
  if(b>=0) {
    vector<int> ret;
    ret.push_back(a), ret.push_back(c), ret.push_back(b), ret.push_back(d);
    ret.push_back(c), ret.push_back(a), ret.push_back(d), ret.push_back(b);
    return ret;
  }
  int prv[1010], pw[1010];
  for(int i=0; i<N; i++) prv[i]=-1, pw[i]=-1;
  vector<pair<int, int>> adj[1010];
  queue<int> q;
  for(int i=0; i<M; i++) adj[U[i]].push_back({V[i], i});
  prv[0]=0, q.push(0);
  while(!q.empty()) {
    int curr=q.front(); q.pop();
    for(auto [next, k]:adj[curr]) if(prv[next]<0) prv[next]=curr, pw[next]=k, q.push(next);
  }
  auto f=[](int a) {return (a&1)?(a-1):(a+1);};
  for(int i=0; i<N; i++) if(prv[i]>=0 && adj[i].size()>=3) {
    vector<int> ret;
    for(int j=i; j; j=prv[j]) ret.push_back(pw[j]);
    reverse(ret.begin(), ret.end());
    for(auto [next, k]:adj[i]) if(f(k)!=pw[i]) ret.push_back(k), ret.push_back(f(k));
    for(auto [next, k]:adj[i]) if(f(k)!=pw[i]) ret.push_back(f(k)), ret.push_back(k);
    for(int j=i; j; j=prv[j]) ret.push_back(pw[j]);
    return ret;
  }
  return false;
}

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