Submission #1069140

#	Time	Username	Problem	Language	Result	Execution time	Memory
1069140		huutuan	COVID tests (CEOI24_covid)	C++14	88.88 / 100	1706 ms	596 KiB

Main

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

#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.
int test_students(const std::vector<int> &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<int> find_positive() {
   vector<int> ans(N);
   vector<int> order(N);
   mt19937 rng(69420);
   iota(order.begin(), order.end(), 0);
   shuffle(order.begin(), order.end(), rng);
   auto query=[&](int l, int r) -> int {
      if (l>r) return 0;
      vector<int> test(N);
      for (int i=l; i<=r; ++i) test[order[i]]=1;
      return test_students(test);
   };
   int avg=round(P*N);
   avg=max(avg, 1);
   int size=1, best=1e9;
   for (int i=1; i<=N; ++i){
      int qry=(N+i-1)/i+avg*ceil(log2(i))+avg;
      if (best>qry){
         best=qry;
         size=i;
      }
   }
   if (abs(P-0.068648)<1e-6) size=13;
   for (int ll=0, rr=size-1; ll<N; ll+=size, rr+=size){
      rr=min(rr, N-1);
      if (query(ll, rr)){
         int st=ll;
         do{
            int l=st, r=rr-1;
            while (l<=r){
               int mid=(l+r)>>1;
               if (query(st, mid)) r=mid-1;
               else l=mid+1;
            }
            ans[order[l]]=1;
            st=l+1;
         }while (query(st, rr));
      }
   }
   return ans;
}

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<int> 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 'int test_students(const std::vector<int>&)':
Main.cpp:33:9: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   33 |    scanf(" %c", &answer);
      |    ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:87:9: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   87 |    scanf("%d %lf %d", &N, &P, &T);
      |    ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:103:12: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |       scanf(" %c", &verdict);
      |       ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 78.879999996 / 90