Submission #1272557

#	Time	Username	Problem	Language	Result	Execution time	Memory
1272557		antonn	COVID tests (CEOI24_covid)	C++20	31.95 / 100	1241 ms	428 KiB

Main

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

// 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:

// 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> ff;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

bool ask(vector<int> &v) {
    vector<bool> query(N, 0);
    for (auto x : v) query[x] = 1;
    return test_students(query);
}


void divide(vector<int> &v) {
    if (v.empty()) return;
    if (v.size() <= 100 && ask(v) == 0) {   
        return;
    }
    if (v.size() == 1) {
        ff[v[0]] = 1;
        return;
    }
    shuffle(v.begin(), v.end(), rng);
    shuffle(v.begin(), v.end(), rng);
    shuffle(v.begin(), v.end(), rng);
    vector<int> left, right;
    for (int i = 0; i < v.size() / 2; ++i) left.push_back(v[i]);
    for (int i = v.size() / 2; i < v.size(); ++i) right.push_back(v[i]);
    divide(left);
    divide(right);
}


vector<bool> find_positive() {
    ff.resize(N);
    for (int i = 0; i < N; ++i) ff[i] = 0;
    vector<int> v;
    for (int i = 0; i < N; ++i) v.push_back(i);
    divide(v);
    return ff;
}


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;
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:28:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:83:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   83 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:99:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   99 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 21.95 / 90