Submission #876840

#	Time	Username	Problem	Language	Result	Execution time	Memory
876840		Kanon	Counting Mushrooms (IOI20_mushrooms)	C++14	94.17 / 100	6 ms	1044 KiB

mushrooms

#include <bits/stdc++.h>
#include "mushrooms.h"
 
using namespace std;
 
int magic = 50;
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;
 
}

• Subtask 1: 94.1667 / 100