Submission #1231146

#	Time	Username	Problem	Language	Result	Execution time	Memory
1231146		alexander707070	COVID tests (CEOI24_covid)	C++20	96.43 / 100	765 ms	420 KiB

Main

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

int N;
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);

    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.

int n,bucket;
double prob;
vector<int> sol;

bool query(int l,int r){
    vector<bool> s(n,0);

    for(int i=l;i<=r;i++)s[i]=true;
    return test_students(s);
}

int bin(int from,int to){
    int l=from-1,r=to,tt;

    while(l+1<r){
        tt=(l+r)/2;

        if(query(from,tt)){
            r=tt;
        }else{
            l=tt;
        }
    }

    return r;
}

void solve(int l,int r){
    if(l>r)return;

    int et=min(r,l+bucket-1);

    if(query(l,et)){
        int pos=bin(l,et);
        sol.push_back(pos);

        solve(pos+1,r);
    }else solve(et+1,r);
}

vector<bool> find_positive(){
    
    n=N; prob=P;
    sol.clear();

    bucket=n;
    double curr=1-prob;
    
    for(int i=2;i<=n;i++){
        curr*=(1-prob);

        if(curr<0.501){
            bucket=i-1; break;
        }
    }

    solve(0,n-1);
    vector<bool> ans(n,0);

    for(int i:sol)ans[i]=true;
    return ans;
}

int main(){

    int T;
    cin>>N>>P>>T;

    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:23:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   23 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:114:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 86.43 / 90