Submission #1218354

#TimeUsernameProblemLanguageResultExecution timeMemory
1218354j_vdd16COVID tests (CEOI24_covid)C++20
58.06 / 100
771 ms404 KiB
#include <cassert> #include <cstdio> #include <string> #include <vector> /// 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'; } /* f(n, p) = 1 + min( (1 - (1 - p)^k) * f(n - k, p) + (1 - p)^k * f(n, 1/k + (1 - 1/k)*p) ) */ /* 1100010010 */ using namespace std; void solve(std::vector<bool>& result, int l, int r) { bool foundPositive = false; int i = l; while (i < r) { double p; if (foundPositive) p = P; else { p = 1.0 / double(r - i) + (1.0 - (1.0 / double(r - i))) * P; } if (abs(p - 1.0) < 0.0000001) { for (int j = i; j < r; j++) result[j] = true; return; } double probAllNegative = 1.0; int count = 0; while (probAllNegative > 0.5) { probAllNegative *= 1.0 - p; count++; } if (0.5 - probAllNegative > probAllNegative / (1.0 - p) - 0.5 && count > 1) count--; count = min(count, r - i); std::vector<bool> mask(N); for (int j = i; j < i + count; j++) { mask[j] = true; } bool res = test_students(mask); if (res && count == 1) { foundPositive = true; result[i] = true; } else if (res) { foundPositive = true; solve(result, i, i + count); } i += count; } } /// 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() { std::vector<bool> answer(N); if (P == 0.0) return answer; if (P == 1.0) { for (int i = 0; i < N; i++) answer[i] = true; return answer; } std::vector<int> students(N); for (int i = 0; i < N; i++) students[i] = i; std::vector<bool> mask(N, true); if (!test_students(mask)) return answer; solve(answer, 0, N); 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:29:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:126:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  126 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:142:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  142 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~
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