Submission #632020

#	Time	Username	Problem	Language	Result	Execution time	Memory
632020		CyanForces	Thousands Islands (IOI22_islands)	C++17	100 / 100	317 ms	36276 KiB

islands

#include "islands.h"

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

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define debug(...) //ignore
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef long double ld;

variant<bool, vi> find_journey(int n, int m, vi u, vi v) {
  vi dead(n);
  vector<set<int>> rg(n), g(n);
  rep(i,0,m) {
    g[u[i]].emplace(i);
    rg[v[i]].emplace(i);
  }

  queue<int> q;
  rep(x,0,n) if(sz(g[x]) == 0) q.emplace(x);

  auto del = [&](int e) {
    g[u[e]].erase(e);
    rg[v[e]].erase(e);
    if(sz(g[u[e]]) == 0) q.emplace(u[e]);
  };

  auto trim = [&]() {
    while(sz(q)) {
      int x = q.front();
      q.pop();
      dead[x] = true;
      vi es(all(rg[x]));
      for(int e : es) del(e);
    }
  };

  trim();
  if(dead[0]) return false;

  vi pth0;
  int x = 0;
  int lst_e = -1;
  while(sz(g[x]) == 1) {
    assert(!dead[x]);
    int e = *g[x].begin();
    pth0.emplace_back(e);

    vi es(all(rg[x]));
    for(int e : es) if(e != lst_e) del(e);
    trim();
    if(dead[0]) return false;

    x = v[e];
    lst_e = e;
  }
  assert(!dead[x]);
  assert(sz(g[x]) >= 2);

  debug(x);
  debug(g[x]);

  vi vis(n);
  vis[x] = 3;
  vi pth1, pth2;

  {
    int e = *g[x].begin();
    pth1.emplace_back(e);
    while(!vis[v[e]]) {
      vis[v[e]] = 1;
      e = *g[v[e]].begin();
      pth1.emplace_back(e);
    }
  }

  {
    int e = *g[x].rbegin();
    pth2.emplace_back(e);
    while(!vis[v[e]]) {
      vis[v[e]] = 2;
      e = *g[v[e]].begin();
      pth2.emplace_back(e);
    }
  }

  debug(pth0, pth1, pth2);
  vi important(n);
  important[x] = 1;
  important[v[pth1.back()]] = 1;
  important[v[pth2.back()]] = 1;

  vector<vi> s1, s2;
  vi cur;
  for(int a : pth1) {
    cur.emplace_back(a);
    if(important[v[a]]) {
      s1.emplace_back(cur);
      cur.clear();
    }
  }

  cur.clear();
  for(int a : pth2) {
    cur.emplace_back(a);
    if(important[v[a]]) {
      s2.emplace_back(cur);
      cur.clear();
    }
  }

  debug(s1);
  debug(s2);

  auto rev = [&](vi v) {
    reverse(all(v));
    return v;
  };

  auto flatten = [&](vector<vi> ve) {
    vi res;
    for(auto& es : ve) for(int e : es) res.emplace_back(e);
    return res;
  };
  auto go = [&](vector<vi> ve) {
    ve.insert(begin(ve),pth0);
    ve.emplace_back(rev(pth0));
    int x = 0;
    vi res = flatten(ve);
    int lst_e = -1;
    for(int e : res) {
      assert(x == u[e]);
      assert(e != lst_e);
      lst_e = e;
      x = v[e];
      swap(u[e], v[e]);
    }
    return res;
  };

  auto do_cyc = [&](vector<vi> s, bool r) {
    vector<vi> g;
    if(sz(s) == 1) g.emplace_back(r ? rev(s[0]) : s[0]);
    else if(sz(s) == 2) {
      g.emplace_back(s[0]);
      g.emplace_back(r ? rev(s[1]) : s[1]);
      g.emplace_back(rev(s[0]));
    }
    else assert(false);
    return flatten(g);
  };

  if(vis[v[s2.back().back()]] != 1) { // separate
    vector<vi> g;
    g.emplace_back(do_cyc(s1,false));
    g.emplace_back(do_cyc(s2,false));
    g.emplace_back(do_cyc(s1,true));
    g.emplace_back(do_cyc(s2,true));
    debug(g);
    return go(g);
  }

  assert(sz(s2) == 1);

  if(v[s1[0].back()] == v[s2[0].back()]) {

    vector<vi> g;

    if(v[s1.back().back()] == x) {
      assert(sz(s1) == 2);
      g.emplace_back(s1[0]);
      g.emplace_back(s1[1]);
      g.emplace_back(s2[0]);
      g.emplace_back(rev(s1[0]));
      g.emplace_back(rev(s1[1]));
      g.emplace_back(rev(s2[0]));
      return go(g);
    }

    auto ss1 = s1;
    ss1.erase(begin(ss1));

    g.emplace_back(s1[0]);
    g.emplace_back(do_cyc(ss1,false));
    g.emplace_back(rev(s1[0]));
    g.emplace_back(s2[0]);
    g.emplace_back(do_cyc(ss1,true));
    g.emplace_back(rev(s2[0]));
    return go(g);
  }


  if(v[s1[1].back()] == v[s2[0].back()]) {
    assert(sz(s1) == 3);
    vector<vi> g;
    g.emplace_back(s1[0]);
    g.emplace_back(s1[1]);
    g.emplace_back(s1[2]);
    g.emplace_back(rev(s1[0]));
    g.emplace_back(s2[0]);
    g.emplace_back(rev(s1[1]));
    g.emplace_back(rev(s1[2]));
    g.emplace_back(rev(s2[0]));
    return go(g);
  }


  return true;

  assert(false);

  return true;
}

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