Submission #1137732

#	Time	Username	Problem	Language	Result	Execution time	Memory
1137732		UmairAhmadMirza	COVID tests (CEOI24_covid)	C++20	56.10 / 100	847 ms	408 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;

// 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);

    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_positive1() {
    vector<bool> answer(N);
    vector<bool> quer(N,0);
    int cur=0;
    int chn=2;
    if(P!=0)
        chn=(1+(1/P))*2;
    while(cur<N){
        int low=cur-1,high=min(N,cur+chn);
        while(high-low>1){
            int mid=(high+low)/2;
            if(high-mid>1)
                mid=(high+mid)/2;
            for(int i=cur;i<=mid;i++)
                quer[i]=1;
            bool b=test_students(quer);
            for(int i=cur;i<=mid;i++)
                quer[i]=0;
            if(b)
                high=mid;
            else
                low=mid;
        }
        if(high!=min(N,cur+chn)){
            answer[high]=1;
            cur=high+1;
        }
        else
            cur+=chn;
    }
    return answer;
}
vector<bool> find_positive() {
    vector<bool> answer(N);
    vector<bool> quer(N,0);
    if(P==0.001){
        return find_positive1();
    }
    int cur=0;
    int chn=2;
    if(P!=0)
        chn=(1+(1/P))*3;
    while(cur<N){
        int low=cur-1,high=min(N,cur+chn);
        while(high-low>1){
            int mid=(high+low)/2;
            // if(high-mid>1)
            //     mid=(high+mid)/2;
            for(int i=cur;i<=mid;i++)
                quer[i]=1;
            bool b=test_students(quer);
            for(int i=cur;i<=mid;i++)
                quer[i]=0;
            if(b)
                high=mid;
            else
                low=mid;
        }
        if(high!=min(N,cur+chn)){
            answer[high]=1;
            cur=high+1;
        }
        else
            cur+=chn;
    }
    return answer;
}
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++) {
        vector<bool> answer = find_positive();
        assert(answer.size() == (size_t)N);

        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:31:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   31 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:110:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  110 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:126:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  126 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 0 / 10
• Subtask 2: 56.1 / 90