Submission #1193852

#	Time	Username	Problem	Language	Result	Execution time	Memory
1193852		mmaiti	COVID tests (CEOI24_covid)	C++20	87.57 / 100	801 ms	408 KiB

Main

#include <bits/stdc++.h>
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';
}

/*// test = false means we know that there is at least 1 positive result in
 * this*/
/*// range*/
int recurse(int L, int R, vector<bool> &ans, bool test) {
  vector<bool> msk(ans.size());
  for (int i = L; i <= R; i++) {
    msk[i] = true;
  }
  int q = 1;
  if (test) {
    q = test_students(msk);
    if (q == 0)
      q = -1;
  }

  if (q == 1) {
    if (L == R) {
      ans[L] = true;
      return L;
    } else {
      int m = (L + R) / 2;
      q = recurse(L, m, ans, true);
      if (q == -1) {
        q = recurse(m + 1, R, ans, false);
      }
    }
  }
  return q;
}
/// 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.
//

long double clamp(long double value, long double lo, long double hi) {
  return max(min(value, hi), lo);
}
std::vector<bool> find_positive() {
  std::vector<bool> answer(N);

  long double cl = 1e-9;
  int init_sz = max((int)(log(0.5) / log(clamp(1 - P, cl, 1 - cl))), 1);
  /*init_sz = 1 << (31 - __builtin_clz(init_sz));*/
  int cur_sz = init_sz;
  int i = 0;
  while (i < N) {
    int nx = recurse(i, min(i + init_sz - 1, N - 1), answer, true);
    if (nx == -1) {
      i = i + init_sz;
    } else {
      i = nx + 1;
    }
  }
  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;
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:28:8: 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:93:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   93 |   scanf("%d %lf %d", &N, &P, &T);
      |   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:109:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  109 |     scanf(" %c", &verdict);
      |     ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 77.57 / 90