| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 1180467 | LucaIlie | COVID tests (CEOI24_covid) | C++20 | 0 ms | 0 KiB |
#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.
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<int> perm;
int expectedPositives;
bool askRange( int l, int r ) {
vector<bool> mask( N, 0 );
for ( int i = l; i <= r; i++ )
mask[perm[i]] = true;
return test_students( mask );
}
vector<int> positive;
const double CST = 0.5;
void divide( int l, int r ) {
bool ans = true, asked = false;
ans &= askRange( l, r );
asked = true;
if ( !ans )
return;
if ( l == r ) {
positive.push_back( perm[l] );
return;
}
int bs = max( 1, (int)(r - l + 1) / (2 * P / (0.001)));
for ( int i = l; i <= r; i += bs )
divide( i, min( i + bs - 1, r ) );
}
const unsigned seed = 20340;
const double EPS = 1e-1;
mt19937 rnd( seed );
vector<bool> find_positive() {
expectedPositives = ceil( N * (P + EPS) );
positive.clear();
perm.clear();
perm.resize( N );
for ( int i = 0; i < N; i++ )
perm[i] = i;
shuffle( perm.begin(), perm.end(), rnd );
divide( 0, N - 1 );
vector<bool> answer( N, 0 );
for ( int i: positive )
answer[i] = true;
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;
}