Submission #1177678

#	Time	Username	Problem	Language	Result	Execution time	Memory
1177678		alexdd	COVID tests (CEOI24_covid)	C++20	50.53 / 100	977 ms	416 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <iostream>
using namespace std;
typedef long double ld;
const int INF = 1e9;
/// You may use:

// The number of students
int N;

// The probability any given student is positive
ld 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.
int prec[1005];
int get_mij(int st, int dr)
{
    return st + prec[dr-st+1] - 1;
}

vector<bool> inter(int le, int ri)
{
    vector<bool> aux(N,0);
    for(int i=le;i<=ri;i++)
        aux[i]=1;
    return aux;
}
std::vector<bool> find_positive()
{
    std::vector<bool> answer(N);

    int poz=0;
    while(poz<N)
    {
        if(!test_students(inter(poz,N-1))) break;

        int st=poz,dr=N-1,ans=-1;
        while(st<=dr)
        {
            int mij = get_mij(st,dr);
            if(test_students(inter(poz,mij)))
            {
                ans = mij;
                dr = mij-1;
            }
            else
            {
                st = mij+1;
            }
        }
        if(ans==-1)
            break;
        answer[ans] = 1;
        poz = ans+1;
    }

    return answer;
}

ld putP[1005],put1P[1005];
void calc_prec()
{
    vector<ld> primu(N+2),pref(N+2,0);
    for(int i=1;i<=N;i++)
    {
        primu[i] = 1;
        for(int j=1;j<i;j++)
            primu[i] = primu[i] * ((ld)1 - P);
        pref[i] = pref[i-1] + primu[i];
        //cout<<i<<" "<<primu[i]<<" primu\n";
    }
    //for(int i=1;i<=N;i++) cout<<i<<" "<<pref[i]<<" pref\n";
    for(int lun=1;lun<=N;lun++)
    {
        ld best=INF;
        int unde=-1;
        for(int i=1;i<=lun;i++)
        {
            ld ple = pref[i];
            ld pri = pref[lun] - pref[i];
            if(abs(ple-pri) < best)
            {
                best = abs(ple-pri);
                unde = i;
            }
        }
        assert(unde!=-1);
        prec[lun] = unde;
        //cout<<lun<<" "<<prec[lun]<<" prec\n";
    }
}

ld ev[1005];
void calc_prec_ver2()
{
    ev[1] = 1;
    prec[1] = 1;
    for(int lun=2;lun<=N;lun++)
    {
        ev[lun] = lun;
        prec[lun] = 1;
        for(int mij=1;mij<lun/2;mij++)
        {
            ld cur = ev[lun-mij]*put1P[mij] + (ev[lun-mij] + ev[mij])*((ld)1 - put1P[mij]) + 1;
            if(cur < ev[lun])
            {
                ev[lun] = cur;
                prec[lun] = mij;
            }
        }
        //cout<<lun<<"  "<<prec[lun]<<"   "<<ev[lun]<<"  prec & ev\n";
    }
}

void calc_prec_ver3()
{
    ev[1] = 1;
    prec[1] = 1;
    for(int lun=2;lun<=N;lun++)
    {
        ev[lun] = INF;
        for(int mij=1;mij<lun;mij++)
        {
            ld cur = abs(put1P[mij] - ((ld)1 - put1P[mij]));
            if(cur < ev[lun])
            {
                ev[lun] = cur;
                prec[lun] = mij;
            }
        }
        //cout<<lun<<"  "<<prec[lun]<<"   "<<ev[lun]<<"  prec & ev\n";
    }
}


int main() {
    int T;
    cin>>N>>P>>T;

    putP[0]=1;
    put1P[0]=1;
    for(int i=1;i<=N+2;i++)
    {
        putP[i] = putP[i-1]*P;
        put1P[i] = put1P[i-1]*((ld)1 - P);
    }

    //calc_prec();
    calc_prec_ver2();
    //calc_prec_ver3();
    //return 0;

    // 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:194:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  194 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 40.53 / 90