Submission #1040782

#	Time	Username	Problem	Language	Result	Execution time	Memory
1040782		elazarkoren	COVID tests (CEOI24_covid)	C++17	75.57 / 100	1438 ms	600 KiB

Main

#include <bits/stdc++.h>
#define x first
#define y second
#define all(v) v.begin(), v.end()
#define chkmin(a, b) a = min(a, b)
#define chkmax(a, b) a = max(a, b)
using namespace std;
typedef long long ll;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pii;
typedef vector<pii> vii;
typedef vector<bool> vb;
/// 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.

//void Solve(int l, int r, vb &ans) {
//    vb test(n);
//    fill(test.begin() + l, test.begin() + r, 1);
//    bool b = test_students(test);
//    if (!b) return;
//    if (l + 1 == r) {
//        ans[l] = 1;
//        return;
//    }
//    Solve(l, (l + r) >> 1, ans);
//    Solve((l + r) >> 1, r, ans);
//}

mt19937 rng(time(0));

int FindNext(int l, int r, vi &ind) {
    vb mask(n);
    for (int i = l; i < r; i++) mask[ind[i]] = 1;
    if (!test_students(mask)) return r;
    for (int i = l; i < r; i++) mask[ind[i]] = 0;
    int begin = l + 1, end = r;
    while (begin < end) {
        int mid = (begin + end) >> 1;
        for (int i = l; i < mid; i++) mask[ind[i]] = 1;
        if (test_students(mask)) end = mid;
        else begin = mid + 1;
        for (int i = l; i < mid; i++) mask[ind[i]] = 0;
    }
    return end - 1;
}

void Solve(int l, int r, vi &ind, vb &ans) {
    while (l < r) {
        int nx = FindNext(l, r, ind);
        ans[nx] = 1;
        l = nx + 1;
    }
}

vb find_positive() {
    vb ans(n);
    vi ind(n);
    iota(all(ind), 0);
    while (!ind.empty()) {
        vi nx;
        shuffle(all(ind), rng);
        int m = ind.size();
        int blocks = min<int>(m, ceil(m * P * 1.3));
        int len = (m + blocks - 1) / blocks;
        for (int i = 0; i < m; i += len) {
//            Solve(i, min(i + len, n), ans);
            int l = i, r = min(i + len, m);
            int j = FindNext(l, r, ind);
            if (j < r) ans[ind[j++]] = 1;
            for (int k = j; k < r; k++) nx.push_back(ind[k]);
        }
        swap(ind, nx);
    }
    return ans;
//    int block = 1000;
//    for (int i = 0; i < n; i += block) Solve(i, i + block, ans);

//    Solve(0, n, answer);
//    vb test(n);
//    for (int i = 0; i < n; i++) {
//        test[i] = 1;
//        answer[i] = test_students(test);
//        test[i] = 0;
//    }
    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++) {
        vb answer = find_positive();
        assert(answer.size() == (size_t)n);

        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:38:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   38 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:123:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  123 |     scanf("%d %lf %d", &n, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:139:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  139 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 0 / 10
• Subtask 2: 75.570000003 / 90