# | Time | Username | Problem | Language | Result | Execution time | Memory |
---|---|---|---|---|---|---|---|
1256854 | chautanphat | COVID tests (CEOI24_covid) | C++20 | 41 ms | 396 KiB |
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
using namespace std;
/// You may use:
// The number of students
int N, lim, cnt;
// 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<bool> answer(1000);
void find_positive(int l, int r) {
if (l > r || cnt >= lim) return;
vector<bool> mask(N);
for (int i = l; i <= r; i++) mask[i] = 1;
int p = test_students(mask);
if (p)
{
if (l == r) answer[l] = 1, cnt++;
else
{
int mid = (l+r)/2;
find_positive(l, mid);
find_positive(mid+1, r);
}
}
}
int main() {
int T;
scanf("%d %lf %d", &N, &P, &T);
lim = N*P*2+3;
// You may perform any extra initialization here.
for (int i = 0; i < T; i++) {
cnt = 0;
for (int j = 0; j < N; j++) answer[j] = 0;
find_positive(0, (N-1)/2);
find_positive((N-1)/2+1, N-1);
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;
}
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