Submission #1044127

#	Time	Username	Problem	Language	Result	Execution time	Memory
1044127		SamAnd	COVID tests (CEOI24_covid)	C++17	0 / 100	3913 ms	344 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
using namespace std;

/// 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(std::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:

void rec(int l, int r, vector<bool>& answer)
{
    vector<bool> v(N, false);
    for (int i = l; i <= r; ++i)
        v[i] = true;
    if (test_students(v) == false)
        return;
    if (l == r)
    {
        answer[l] = true;
        return;
    }
    int m = (l + r) / 2;
    rec(l, m, answer);
    rec(m + 1, r, answer);
}

void solv0(vector<bool>& answer)
{
    int s = 0;
    while (s < N)
    {
        int l = s, r = N - 1;
        vector<bool> v(N, false);
        for (int i = l; i <= r; ++i)
            v[i] = true;
        if (!test_students(v))
            break;
        int u;
        while (l <= r)
        {
            int m = (l + r) / 2;
            vector<bool> v(N, false);
            for (int i = s; i <= m; ++i)
                v[i] = true;
            if (test_students(v))
            {
                u = m;
                r = m - 1;
            }
            else
                l = m + 1;
        }
        answer[u] = true;
        s = u + 1;
    }
}

// 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.
std::vector<bool> find_positive() {
    std::vector<bool> answer(N, false);
    //rec(0, N - 1, answer);
    solv0(answer);
    return answer;
}

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);
    }

    return 0;
}

// 1000 0.001 300

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:30:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:97:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   97 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:113:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  113 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp: In function 'void solv0(std::vector<bool>&)':
Main.cpp:80:11: warning: 'u' may be used uninitialized in this function [-Wmaybe-uninitialized]
   80 |         s = u + 1;
      |         ~~^~~~~~~

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