Submission #834896

#	Time	Username	Problem	Language	Result	Execution time	Memory
834896		Username4132	Thousands Islands (IOI22_islands)	C++17	35 / 100	52 ms	21696 KiB

islands

#include "islands.h"

#include <variant>
#include<iostream>
#include <vector>
#include<cassert>
using namespace std;
using pii = pair<int, int>;
#define forn(i, n) for(int i=0; i<(int)n; ++i)
#define PB push_back
#define F first
#define S second

const int MAXN = 100010;
int n, m, cur, stpos[MAXN];
bool vis[MAXN], blocked[MAXN], inst[MAXN];
vector<int> st, se;
vector<pii> g[MAXN];

bool dfs2(int v){
  inst[v]=true;
  vis[v]=true;
  for(pii to:g[v]) if(!vis[to.F] && !blocked[to.F]) {
    bool ret = dfs2(to.F);
    if(ret) return true;
  }
  else if((inst[to.F] || stpos[to.F]!=-1) && !blocked[to.F] && to.S != se[cur]){
    return true;
  }
  inst[v]=false;
  return false;
}

int dfs1(int v){
  stpos[v]=(int)st.size();
  st.PB(v);
  vis[v]=true;
  for(pii to:g[v]) if(!vis[to.F] && !blocked[to.F]){
    se.PB(to.S);
    int ret = dfs1(to.F);
    if(ret) return ret;
  }
  else if(stpos[to.F]!=-1){
    while(cur<=stpos[to.F]){
      bool ret = dfs2(st[cur]);
      if(ret) return 1;
      blocked[st[cur]]=true;
      ++cur;
    }
  }
  if((int)st.size() <= cur+1) return 2;
  st.pop_back();
  se.pop_back();
  stpos[v]=-1;
  return 0;
}

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
  n=N, m=M;
  forn(i, n) stpos[i]=-1;
  forn(i, m) g[U[i]].PB({V[i], i});

  int ret = dfs1(0);
  if(ret==1){
    vector<int> ans;
    return ans;
  }
  return false;
}

• 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