Submission #629580

#	Time	Username	Problem	Language	Result	Execution time	Memory
629580		abeker	Thousands Islands (IOI22_islands)	C++17	100 / 100	333 ms	36856 KiB

islands

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

typedef pair <vector <int>, vector <int>> pvv;

void output(const vector <int> &v) {
  for (auto it : v)
    printf("%d ", it);
  puts("");
}

void output(const pvv &p) {
  output(p.first);
  output(p.second);
}

bool check(int M, vector <int> u, vector <int> v, vector <int> s) {
  int curr = 0, prev = -1;
  vector <int> occ(M);
  for (auto it : s) {
    if (it == prev)
      return false;
    if (u[it] != curr)
      return false;
    curr = v[it];
    swap(u[it], v[it]);
    occ[it] ^= 1;
    prev = it;
  }
  return !curr && !count(occ.begin(), occ.end(), 1);
}

vector <int> min_rot(vector <int> v) {
  rotate(v.begin(), min_element(v.begin(), v.end()), v.end());
  return v;
}

variant <bool, vector <int>> find_journey(int N, int M, vector <int> u, vector <int> v) {
  queue <int> sinks;
  vector <set <int>> in(N), out(N);
  for (int i = 0; i < M; i++) {
    out[u[i]].insert(i);
    in[v[i]].insert(i);
  }
  auto refresh = [&](int x) {
    if (out[x].empty())
      sinks.push(x);
  };
  for (int i = 0; i < N; i++)
    refresh(i);
  int curr = 0;
  vector <int> sofar;
  while (1) {
    auto remove = [&](int x) {
      for (auto it : in[x]) {
        out[u[it]].erase(it);
        refresh(u[it]);
      }
      for (auto it : out[x])
        in[v[it]].erase(it);
    };
    for (; !sinks.empty(); sinks.pop()) {
      if (sinks.front() == curr)
        return false;
      remove(sinks.front());
    }
    if (out[curr].size() == 1) {
      int edge = *out[curr].begin();
      remove(curr);
      curr = v[edge];
      sofar.push_back(edge);
    }
    else {
      assert(out[curr].size() >= 2);
      auto find_cycle = [&](int x, int e, bool b) {
        int y = x;
        vector <int> path = {e};
        vector <bool> bio(N);
        bio[x] = b;
        for (x = v[e]; !bio[x]; x = v[e]) {
          path.push_back(e = *out[x].begin());
          bio[x] = true;
        }
        int last = -1;
        for (int i = 0; i < path.size(); i++) {
          if (y == x)
            last = i;
          y = v[path[i]];
        }
        vector <int> tail, cycle;
        for (int i = 0; i < path.size(); i++)
          if (i < last)
            tail.push_back(path[i]);
          else
            cycle.push_back(path[i]);
        return pvv(tail, cycle);
      };
      auto it = out[curr].begin();
      pvv cyc1 = find_cycle(curr, *it++, true);
      pvv cyc2 = find_cycle(curr, *it++, false);
      //output(cyc1);
      //output(cyc2);
      vector <int> sol;
      auto append = [&](vector <int> &v) {
        sol.insert(sol.end(), v.begin(), v.end());
        reverse(v.begin(), v.end());
      };
      append(sofar);
      bool eq = min_rot(cyc1.second) == min_rot(cyc2.second);
      for (int i = 0; i < 2; i++) {
        auto traverse = [&](pvv &p1, pvv &p2) {
          append(p1.first);
          append(p1.second);
          if (eq)
            reverse(p2.second.begin(), p2.second.end());
          append(p1.first);
        };
        traverse(cyc1, cyc2);
        traverse(cyc2, cyc1);
      }
      append(sofar);
      assert(check(M, u, v, sol));
      return sol;
    }
  }
}

Compilation message (stderr)

islands.cpp: In lambda function:
islands.cpp:86:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   86 |         for (int i = 0; i < path.size(); i++) {
      |                         ~~^~~~~~~~~~~~~
islands.cpp:92:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   92 |         for (int i = 0; i < path.size(); i++)
      |                         ~~^~~~~~~~~~~~~

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