Submission #304110

#	Time	Username	Problem	Language	Result	Execution time	Memory
304110		llaki	Counting Mushrooms (IOI20_mushrooms)	C++17	0 / 100	2 ms	256 KiB

mushrooms

#include <math.h>
#include "mushrooms.h"

int count_mushrooms(int n) {
	std::vector<int> m;
	int ans = 1;
	if (n <= 226) {
		for (int i = 1; i < n; i++) {
			m = {0, i};
			int res = use_machine(m);
			if (res == 0) ans++;
		}
		return ans;
	}
	int k = (int) (sqrt(n / 2));
	// 0, 1, ..., k
	// 0, k + 1, ..., 2k
	// 0, 2k + 1, ..., 3k
	// 0, 3k + 1, ..., 4k
	//...
	// bk + 1 <= n - 1
	int B = (n - 2) / k;
	// 0 ... B
	std::vector<int> answers;
	std::vector<int> ones, zeroes;
	int known[20001];
	for (int q = 0; q <= B; q++) {
		std::vector<int> query;
		query.push_back(0);
		int largest = 0;
		for (int i = 1; i <= k; i++) {
			int num = i + q * k;
			if (num >= n) break;
			largest = num;
			query.push_back(num);
		}
		int res = use_machine(m);
		answers.push_back(res);
		if (res == 0) {
			zeroes.push_back(largest);
		} else {
			ones.push_back(largest);
		}
		known[largest] = 1;
	}
	int countZeroes = 1 + zeroes.size();
	std::vector<int> unknown;
	for (int i = 1; i < n; i++) {
		if (known[i] != 1) {
			unknown.push_back(i);
		}
	}
	std::vector<int> indices = (ones.size() > zeroes.size() ? ones : zeroes);
	bool isOne = ones.size() > zeroes.size();
	int s = indices.size();
	for (int i = 0; i < unknown.size(); i++) {
		std::vector<int> query;
		query.push_back(indices[0]);
		for (int j = 1; j < s && i + j - 1 < unknown.size(); j++) {
			query.push_back(unknown[i + j - 1]);
			query.push_back(indices[j]);
		}
		if (query.size() < 2) break;
		int res = use_machine(query);
		if (isOne) {
			int ones = res / 2;
			countZeroes += s - 1 - ones;
		} else {
			countZeroes += res / 2;
		}
		i = i + s - 2;
	}
	return countZeroes;
}

Compilation message (stderr)

mushrooms.cpp: In function 'int count_mushrooms(int)':
mushrooms.cpp:56:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |  for (int i = 0; i < unknown.size(); i++) {
      |                  ~~^~~~~~~~~~~~~~~~
mushrooms.cpp:59:38: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   59 |   for (int j = 1; j < s && i + j - 1 < unknown.size(); j++) {
      |                            ~~~~~~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 100