Submission #1256852

#	Time	Username	Problem	Language	Result	Execution time	Memory
1256852		chautanphat	COVID tests (CEOI24_covid)	C++20	10 / 100	7 ms	396 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>

using namespace std;

/// You may use:

// The number of students
int N, lim, cnt;

// 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:

// 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> answer(1000);

void find_positive(int l, int r) {
    if (l > r || cnt >= lim) return;
    vector<bool> mask(N);
    for (int i = l; i <= r; i++) mask[i] = 1;
    int p = test_students(mask);
    if (p)
    {
        if (l == r) answer[l] = 1, cnt++;
        else
        {
            int mid = (l+r)/2;
            find_positive(l, mid);
            find_positive(mid+1, r);
        }
    }
}

int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);
    lim = N*P*2;

    // You may perform any extra initialization here.

    for (int i = 0; i < T; i++) {
        cnt = 0;
        for (int j = 0; j < N; j++) answer[j] = 0;
        find_positive(0, (N-1)/2);
        find_positive((N-1)/2+1, N-1);
        
        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;
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:31:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   31 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:63:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   63 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:82:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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