Submission #1037927

#	Time	Username	Problem	Language	Result	Execution time	Memory
1037927		MilosMilutinovic	COVID tests (CEOI24_covid)	C++14	100 / 100	1716 ms	760 KiB

Main

#include <bits/stdc++.h>

using namespace std;

const double prob[] = {0.001, 0.005256, 0.011546, 0.028545, 0.039856, 0.068648, 0.104571, 0.158765, 0.2};
const int bs[] = {1000, 190, 86, 23, 17, 9, 7, 5, 3};

/// 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:

// 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() {
  vector<int> ids(N);
  iota(ids.begin(), ids.end(), 0);
  vector<bool> res(N);
  int B = 1;
  for (int i = 0; i < 9; i++) {
    if (P == prob[i]) {
      B = bs[i];
    }
  }
  while (!ids.empty()) {
    int n = (int) ids.size();
    vector<bool> qv(N);
    for (int i = 0; i < min(n, B); i++) {
      qv[ids[i]] = true;
    }
    if (!test_students(qv)) {
      vector<int> new_vec;
      for (int i = min(n, B); i < n; i++) {
        new_vec.push_back(ids[i]);
      }
      ids = new_vec;
      continue;
    }
    int low = 0, high = min(n, B) - 1;
    while (low < high) {
      int mid = (low + high - 1) >> 1;
      qv = vector<bool>(N, false);
      for (int i = 0; i <= mid; i++) {
        qv[ids[i]] = true;
      }
      if (test_students(qv)) {
        high = mid;
      } else {
        low = mid + 1;
      }
    }
    res[ids[high]] = true;
    vector<int> new_vec;
    for (int i = high + 1; i < n; i++) {
      new_vec.push_back(ids[i]);
    }
    ids = new_vec;
  }
  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);
    }

    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:32:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   32 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:91:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   91 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:107:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  107 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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