Submission #1272565

#	Time	Username	Problem	Language	Result	Execution time	Memory
1272565		antonn	COVID tests (CEOI24_covid)	C++20	86.25 / 100	825 ms	404 KiB

Main

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

// 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> ff;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

bool ask(int l, int r) {
    vector<bool> query(N, 0);
    for (int i = l; i <= r; ++i) query[i] = 1;
    return test_students(query);
}

int getFirst(int l, int r) {
    if (l == r) return l;
    int m = (l + r) / 2;
    if (ask(l, m)) {
        return getFirst(l, m);
    } else {
        return getFirst(m + 1, r);
    }
}

vector<bool> find_positive() {
    ff.resize(N);
    for (int i = 0; i < N; ++i) ff[i] = 0;
    
    int B = 0;
    
    if (P == 0.001) {
        B = 200;
    } else if (P == 0.005256) {
        B = 160;
    } else if (P == 0.011546) {
        B = 80;
    } else if (P == 0.028545) {
        B = 30;
    } else if (P == 0.039856) {
        B = 20;
    } else if (P == 0.068648) {
        B = 10;
    } else if (P == 0.104571) {
        B = 6;
    } else if (P == 0.158765) {
        B = 4;
    } else if (P == 0.2) {
        B = 2;
    }
    
    int pos = 0;
    while (pos < N) {
        int l = pos;
        int r = min(pos + B, N - 1);
        if (ask(l, r)) {
            int x = getFirst(l, r);
            ff[x] = 1;
            pos = x + 1;
        } else {
            pos = r + 1;
        }
    }
    
    return ff;
}


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:28:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:103:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:119:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  119 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 76.25 / 90