Submission #1193127

#	Time	Username	Problem	Language	Result	Execution time	Memory
1193127		Unforgettablepl	COVID tests (CEOI24_covid)	C++20	99.20 / 100	753 ms	408 KiB

Main

#include <bits/stdc++.h>
using namespace std;

/// You may use:

// The number of students
int N;
int jump;
// 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(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> find_positive() {
    vector<bool> answer(N);
    vector<int> idxes(N);
    iota(idxes.begin(),idxes.end(),0ll);
    shuffle(idxes.begin(),idxes.end(),mt19937(38945238));
    auto query = [&](int a,int b){
        vector<bool> q(N);
        for(int i=a;i<=b;i++)q[idxes[i]]=true;
        return test_students(q);
    };
    auto getBeforeNext = [&](int x){
        if(x==N-1)return N-1;
        while(true){
            int tryX = min(x+jump,N-1);
            if(query(x+1,tryX)){
                int L = x+1;
                int R = tryX;
                while(L<R){
                    int siz = R-L+1;
                    long double invP = 1.0-P;
                    int pick = llroundl((logl(1+powl(invP,siz))-logl(2))/logl(invP));
                    pick+=L-1;
                    pick = min(max(pick,L),R-1);
                    if(query(L,pick)){
                        R = pick;
                    } else {
                        L = pick+1;
                    }
                }
                return L-1;
            } else {
                x=tryX;
                if(x==N-1)return N-1;
            }
        }
    };
    int x = getBeforeNext(-1);
    while(x!=N-1){
        answer[idxes[++x]]=true;
        x = getBeforeNext(x);
    }
    return answer;
}

int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);
    // You may perform any extra initialization here.
    jump = max(1ll,llroundl(-1.0/log2l(1-P)));
    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:27:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   27 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:83:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   83 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:98:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   98 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 89.2 / 90