Submission #1073557

#	Time	Username	Problem	Language	Result	Execution time	Memory
1073557		ProtonDecay314	COVID tests (CEOI24_covid)	C++17	10 / 100	933 ms	596 KiB

Main

// AM + DG
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pll;
typedef vector<pll> vpll;
typedef pair<int, int> pi;
typedef vector<pi> vpi;
typedef vector<bool> vb;
#define fi first
#define se second
#define IOS cin.tie(nullptr); cout.tie(nullptr); ios_base::sync_with_stdio(false)
#define pb push_back
#define INF(dtype) numeric_limits<dtype>::max()
#define NINF(dtype) numeric_limits<dtype>::min()

/// You may use:

// The number of students
int N;

// The probability any given student is positive
double P;

// The size of the set that maximizes entropy/"surprise"
int k;

// 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& answer) {
//     vb mask(N, false);
    
//     for(int i = l; i <= r; i++) mask[i] = true;
//     bool res = test_students(mask);

//     if(!res) {
//         for(int i = l; i <= r; i++) answer[i] = false;
//     } else if(l == r) {
//         answer[l] = true;
//     } else {
//         int m = (l + r) >> 1;
//         solve(l, m, answer);
//         solve(m + 1, r, answer);
//     }
// }

std::vector<bool> find_positive() {
    std::vector<bool> answer(N);

    // solve(0, N - 1, answer);

    for(int bi = 0; bi * k < N; bi++) {
        // Current block is...
        int l = bi * k, r = (bi + 1) * k - 1;
        r = min(r, N - 1);

        vb mask(N, false);

        for(int i = l; i <= r; i++) {
            mask[i] = true;
        }

        bool is_pos = test_students(mask);

        for(int i = l; i <= r; i++) {
            mask[i] = false;
        }

        if(is_pos) {
            // brute force
            for(int i = l; i <= r; i++) {
                mask[i] = true;

                answer[i] = test_students(mask);

                mask[i] = false;
            }
        } else {
            for(int i = l; i <= r; i++) {
                answer[i] = false;
            }
        }
    }

    return answer;
}

int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);

    // You may perform any extra initialization here.

    // Compute size of set that maximizes "surprisal"
    k = max((int)lround(-1.0 / log2(1.0 - P)), 1);

    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:47:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   47 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:118:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  118 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:137:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  137 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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