| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 1269642 | Faggi | COVID tests (CEOI24_covid) | C++20 | 0 ms | 0 KiB |
#include <bits/stdc++.h>
#define ll long long
#define sz(x) int(x.size())
#define forn(i,n) for(i=0; i<n; i++)
#define all(x) x.begin(),x.end()
#define pb push_back
#define mp make_pair
#define fr first
#define se second
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<bool>answer;
void calc(ll l, ll r)
{
if(l>r)
return;
// Test whole group
std::vector<bool> t(N, false);
for (int i = l; i <= r; ++i) t[i] = true;
if (!test_students(t)) return;
// Positive: binary search in group
ll pos = -1, in_s = l;
while (l <= r) {
ll piv = (l + r) / 2;
std::fill(t.begin(), t.end(), false);
for (ll i = in_s; i <= piv; ++i) t[i] = true;
if (test_students(t)) {
pos = piv;
r = piv - 1;
} else l = piv + 1;
}
if (pos != -1) {
answer[pos] = true;
calc(pos + 1, N-1); // Recurse suffix
}
}
std::vector<bool> find_positive2()
{
ll n=N;
vector<bool> s(n, 0);
vector<bool>ans(n,0);
for(int i=0; i<n; i++)
{
s[i]=1;
if(test_students(s))
{
ans[i]=1;
}
s[i]=0;
}
return ans;
}
std::vector<bool> find_positive() {
if(P>=0.1)
return find_positive2();
answer.resize(N,0);
calc(0,N-1);
return answer;
}