Submission #1285059

#	Time	Username	Problem	Language	Result	Execution time	Memory
1285059		weebyeah	COVID tests (CEOI24_covid)	C++20	69.42 / 100	997 ms	420 KiB

Main

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

#define Umazing ios::sync_with_stdio(false); cin.tie(nullptr);
#define ll long long

#define pii pair<int, int>
#define pll pair<ll, ll>

/// You may use:

// The number of students
int N;

// The probability any given student is positive
double P;

// This function performs a test on a subset of samples.
// Its argument is a vector of Booleans of length N,
// where the i-th element is true if the i-th sample should be added to the mix.
// It returns true if (and only if) at least one of the samples in the mix is positive.
bool test_students(vector<bool> mask)
{
    assert(mask.size() == (size_t)N);

    std::string mask_str(N, ' ');
    for (int i = 0; i < N; i++)
        mask_str[i] = mask[i] ? '1' : '0';

    printf("Q %s\n", mask_str.c_str());
    fflush(stdout);

    char answer;
    scanf(" %c", &answer);
    return answer == 'P';
}

/// You should implement:

// This function will be called once for each test instance.
// It should use test_students to determine which samples are positive.
// It must return a vector of Booleans of length N,
// where the i-th element is true if and only if the i-th sample is positive.
vector<bool> find_positive()
{
    vector<int> sta(N);

    while (true)
    {
        int cc = 0;
        for (int i = 0; i < N; i++)
        {
            if (sta[i] == 0)
                cc++;
        }

        if (cc == 0)
            break;

        int g;
        if (P <= 0.0)
            g = cc;
        else if (P >= 1.0)
            g = 1;
        else
        {
            double dd = log(1.0 - P);
            if (dd == 0.0)
                g = 1;
            else
            {
                int cand = floor(log(0.5) / dd);

                if (cand < 1)
                    cand = 1;

                if (cand > cc)
                    cand = cc;

                g = cand;
            }
        }

        if (g < 1)
            g = 1;

        if (g > cc)
            g = cc;

        vector<int> gr;
        for (int i = 0; i < N && gr.size() < g; i++)
        {
            if (sta[i] == 0)
                gr.push_back(i);
        }

        vector<bool> m(N, false);
        for (int idx: gr)
        {
            m[idx] = true;
        }

        bool ps = test_students(m);

        if (!ps)
        {
            for (int x: gr)
            {
                sta[x] = 1;
            }

            continue;
        }

        while (!gr.empty())
        {
            vector<int> gg = gr;

            while (gg.size() > 1)
            {
                int k = gg.size() / 2;
                vector<int> l(gg.begin(), gg.begin() + k);
                vector<int> r(gg.begin() + k, gg.end());

                vector<bool> ml(N, false);
                for (int x: l) 
                {
                    ml[x] = true;
                }

                bool lp = test_students(ml);

                if (lp)
                    gg.swap(l);
                else
                {
                    for (int x: l) 
                    {
                        sta[x] = 1;
                    }

                    gg.swap(r);
                }
            }

            int pos = gg[0];
            sta[pos] = 2;

            vector<int> grn;
            for (int x: gr)
            {
                if (x != pos)
                    grn.push_back(x);
            }

            if (grn.empty())
                break;

            vector<bool> mrem(N, false);
            for (int x: grn)
            {
                mrem[x] = true;
            }

            bool mm = test_students(mrem);

            if (!mm)
            {
                for (int x: grn)
                {
                    sta[x] = 1;
                }

                gr.clear();

                break;
            }
            else
                gr.swap(grn);
        }
    }

    vector<bool> res(N, false);
    for (int i = 0; i < N; i++)
    {
        res[i] = (sta[i] == 2);
    }

    return res;
}


int main() 
{
    int T;
    scanf("%d %lf %d", &N, &P, &T);

    // You may perform any extra initialization here.

    for (int i = 0; i < T; i++) {
        std::vector<bool> answer = find_positive();
        assert(answer.size() == (size_t)N);

        std::string answer_str(N, ' ');
        for (int j = 0; j < N; j++)
            answer_str[j] = answer[j] ? '1' : '0';

        printf("A %s\n", answer_str.c_str());
        fflush(stdout);

        char verdict;
        scanf(" %c", &verdict);
        if (verdict == 'W')
            exit(0);
    }
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:34:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   34 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:196:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  196 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:212:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  212 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 59.42 / 90