Submission #834203

#	Time	Username	Problem	Language	Result	Execution time	Memory
834203		finn__	Counting Mushrooms (IOI20_mushrooms)	C++17	87.60 / 100	10 ms	460 KiB

mushrooms

#include <bits/stdc++.h>

#include "mushrooms.h"

using namespace std;

constexpr size_t M = 80;

int count_mushrooms(int n)
{
    // Binary search for another A.

    bool second_is_b = use_machine({0, 1});
    int a = 1, b = second_is_b ? n : 1, c = 0, lower_limit = 0;
    while (a < b)
    {
        int mid = (a + b) / 2;
        vector<int> v(mid - lower_limit + 1);
        iota(v.begin(), v.end(), lower_limit);
        int x = use_machine(v) + c;
        if (x >= 2)
            b = mid;
        else
            a = mid + 1, lower_limit = mid, c = x;
    }

    if (a == n)
        return 1;
    int last_known = a, num_a = 2;

    // Search for at least M A or B.
    vector<int> a_indices = {0, a}, b_indices;
    for (int i = last_known + 1; i + 1 < n; i += 2)
    {
        int x = use_machine({0, i, a, i + 1});
        last_known = i + 1;
        if (x & 1)
            b_indices.push_back(i + 1);
        else
            a_indices.push_back(i + 1), ++num_a;
        if (x & 2)
            b_indices.push_back(i);
        else
            a_indices.push_back(i), ++num_a;

        if (a_indices.size() >= M || b_indices.size() >= M)
            break;
    }

    if (last_known == n - 2)
    {
        num_a += !use_machine({0, n - 1});
        ++last_known;
    }
    if (last_known == n - 1)
        return num_a;

    {
        for (int i = last_known + 1; i < n;)
        {
            vector<int> &r = a_indices.size() > b_indices.size() ? a_indices : b_indices;
            size_t m = r.size();
            bool flag = a_indices.size() > b_indices.size();
            vector<int> v;
            for (int j = 0; j < m && i + j < n; ++j)
            {
                v.push_back(r[j]);
                v.push_back(i + j);
            }

            int x = use_machine(v);
            num_a += flag ? v.size() / 2 - (x + 1) / 2 : (x + 1) / 2;
            (((x & 1) ^ flag) ? a_indices : b_indices).push_back(min<size_t>(n, i + m - 1));
            i += m;
        }
    }

    return num_a;
}

Compilation message (stderr)

mushrooms.cpp: In function 'int count_mushrooms(int)':
mushrooms.cpp:65:31: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
   65 |             for (int j = 0; j < m && i + j < n; ++j)
      |                             ~~^~~

• Subtask 1: 87.5969 / 100