Submission #1269667

#	Time	Username	Problem	Language	Result	Execution time	Memory
1269667		Faggi	COVID tests (CEOI24_covid)	C++20	27.45 / 100	1041 ms	440 KiB

Main

#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;
    vector<bool>t(N,0);
    ll i, piv, pos=-1, in=l;
    for (i = l; i <= r; ++i)
        t[i] = 1;
    if (!test_students(t))
        return;
    while(l<=r)
    {
        piv=(l+r)/2;
        for(i=0; i<sz(t); i++)
            t[i]=0;
        for(i=in; i<=piv; i++)
            t[i]=1;
        if(test_students(t))
        {
            pos=piv;
            r=piv-1;
        }
        else
            l=piv+1;
    }
    if(pos==-1)
        return;
    answer[pos]=1;
    calc(pos+1,N-1);

}
void group_search(ll start, ll end)
{
    if (start > end)
        return;
    // Test whole group
    std::vector<bool> t(N, false);
    for (int i = start; i <= end; ++i)
        t[i] = true;
    if (!test_students(t))
        return;
    // Positive: binary search in group
    ll l = start, r = end, pos = -1, in_s = start;
    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;
        group_search(pos + 1, end); // 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.assign(N, false);
    calc(0, N - 1);
    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:35:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   35 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:140:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  140 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:157:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  157 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 17.45 / 90