Submission #876837

#TimeUsernameProblemLanguageResultExecution timeMemory
876837KanonCounting Mushrooms (IOI20_mushrooms)C++14
93.78 / 100
6 ms740 KiB
#include <bits/stdc++.h>
#include "mushrooms.h"

using namespace std;

int magic = 57;
const int bound = 226;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
// generate random number between l, r : uniform_int_distribution<long long>(l, r)(rng)
// random shuffle : shuffle(.begin(), .end(), rng)

int count_mushrooms(int n) {

  if (n <= bound + 1) {
    int ret = 1;
    for (int i = 1; i < n; i++) {
      ret += use_machine({0, i}) ^ 1;
    }
    return ret;
  }

  vector<int> a(n, -1);
  a[0] = 0;

  vector<int> order(2 * magic);
  iota(order.begin(), order.end(), 1);

  int cnt = 2 * magic + 1;
  vector<int> zeros, ones;
  zeros.push_back(0);

  while (zeros.size() < 3 && ones.size() < 3) {

    int st = use_machine({0, cnt++});
    a[cnt - 1] = a[0] ^ (st & 1);

    if (a[cnt - 1] == 0) zeros.push_back(cnt - 1);
    else ones.push_back(cnt - 1);

  }

  int p1, p2, p3, bit;
  if (zeros.size() >= 3) {
    p1 = zeros[0], p2 = zeros[1], p3 = zeros[2], bit = 0;
  } else {
    p1 = ones[0], p2 = ones[1], p3 = ones[2], bit = 1;
  }
  zeros.clear();
  ones.clear();

  auto calc = [&](vector<int> d) {

    vector<int> que = {p1, d[0], p2};
    if (d.size() > 1) {
      que.push_back(d[1]);
      que.push_back(p3);
    }
    que.push_back(cnt++);

    int st = use_machine(que);

    a[cnt - 1] = bit ^ (st & 1);

    st -= st & 1;
    st >>= 1;
    if (bit == 1) st = d.size() - st;
    return st;

  };

  function<void(vector<int>)> solve = [&](vector<int> pos) {
    
    if (pos.empty()) return;
    if (pos.size() == 1) {
      int p = pos[0];
      a[p] = calc({p});
      return;
    }

    shuffle(pos.begin(), pos.end(), rng);
    vector<int> L, R;
    for (int i = 0; i + 1 < (int) pos.size(); i += 2) {

      int sum = calc({pos[i], pos[i + 1]});

      if (sum == 1) {
        L.push_back(pos[i]);
        R.push_back(pos[i + 1]);
      } else {
        a[pos[i]] = a[pos[i + 1]] = sum >> 1;
      }

    }

    if (pos.size() & 1) {

      int p = pos.back();
      a[p] = calc({p});

    }

    solve(L);
    for (int i = 0; i < (int) L.size(); i++) {

      int l = L[i], r = R[i];
      assert(a[l] != -1);

      a[r] = a[l] ^ 1;

    }

  };
  solve(order);

  int ret = 0;
  for (int i = 0; i < n; i++) {
    ret += a[i] == 0;
    if (a[i] == 0) zeros.push_back(i);
    if (a[i] == 1) ones.push_back(i);
  }

  while (cnt < n) {

    int len = min(n - cnt, (int) max(zeros.size(), ones.size()));
    vector<int> ids = zeros.size() >= ones.size() ? zeros : ones;

    vector<int> que;
    for (int i = 0; i < len; i++) {
      que.push_back(ids[i]);
      que.push_back(cnt++);
    }

    int st = use_machine(que);

    if (ids == ones) {

      a[cnt - 1] = 1 ^ (st & 1);
      ret += a[cnt - 1] == 0;
      st -= a[cnt - 1] == 0;

      if (a[cnt - 1] == 0) zeros.push_back(cnt - 1);
      else ones.push_back(cnt - 1);

      assert(st % 2 == 0);
      ret += st >> 1;

    } else {

      a[cnt - 1] = 0 ^ (st & 1);
      ret += a[cnt - 1] == 0;
      st -= a[cnt - 1] == 1;

      if (a[cnt - 1] == 0) zeros.push_back(cnt - 1);
      else ones.push_back(cnt - 1);

      assert(st % 2 == 0);
      ret += (len - 1) - (st >> 1);
    }
  }
  return ret;

}
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