Submission #1050989

#	Time	Username	Problem	Language	Result	Execution time	Memory
1050989		n1k	COVID tests (CEOI24_covid)	C++17	87.57 / 100	1558 ms	344 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bits/stdc++.h>

using namespace std;

/// You may use:

// The number of students
int N, T;

// 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.
std::vector<bool> find_positive() {
    std::vector<bool> answer(N);
    vector<int> a(N);
    iota(a.begin(), a.end(), 0);
    shuffle(a.begin(), a.end(), mt19937{std::random_device{}()});

    int take = T == 1 ? 1 : max(1., (1/P) * 2./3);

    for(int i=0; i<N;){
        vector<bool> mask(N); 
        for(int j=0; j<take and i+j<N; j++){
            mask[i+j] = 1;
        }
        if(test_students(mask)){
            int lb = i, rb = min(i + take - 1, N-1);
            while(lb<rb){
                int mb = (lb+rb)/2;
                mask.assign(N, 0);
                for(int j=lb; j<=mb; j++) mask[j]=1;
                if(test_students(mask)){
                    rb = mb;
                }else{
                    lb = mb + 1;
                }
            }
            answer[lb]=1;
            i = lb + 1;
        }else{
            i += take;
        }
    }

    return answer;
}

int main() {
    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:32:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   32 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:78:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   78 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:94:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   94 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 77.570000001 / 90