Submission #1199459

#	Time	Username	Problem	Language	Result	Execution time	Memory
1199459		lighton	COVID tests (CEOI24_covid)	C++20	56.04 / 100	1599 ms	5296 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include<bits/stdc++.h>
#define pb push_back
#define all(v) v.begin(),v.end()
#define forf(i,s,e) for(int i = s; i<=e; i++)
#define forb(i,s,e) for(int i = s; i>=e; i--)
#define idx(i,v) lower_bound(all(v),i)-v.begin()
#define comp(v) v.erase(unique(all(v)),v.end())
#define sz(v) (int)v.size()
#define fs first
#define se second
#define SP << " " <<
#define LN << "\n"
#define IO cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);
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(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.

double a[1001];
pair<double,int> dp[1001][2];
vector<bool> answer,v;

void findn(){
    a[0] = 1;
    forf(i,1,N) a[i] = a[i-1]*(1-P);

    dp[1][1] = {0,0};
    dp[1][0] = {1,1};
    forf(i,2,N){
        dp[i][1] = {1e18,0};
        dp[i][0] = {1e18,0};
        forf(j,1,i-1){
            double p = max(1-a[j], ((double)j)/i);
            double e = 1+p*(dp[j][1].fs + dp[i-j][0].fs) + (1-p)*(dp[i-j][1].fs);
            dp[i][1] = min(dp[i][1], {e,j});
        }
        forf(j,1,i){
            double e = 1+(1-a[j])*(dp[j][1].fs + dp[i-j][0].fs) + a[j]*dp[i-j][0].fs;
            dp[i][0] = min(dp[i][0], {e,j});
        }
    }
}

void go(vector<int> c, int d){
    if(sz(c) == 1 && d == 1) {
        answer[c[0]] = 1; return;
    }
    if(sz(c) == 0) return;

    random_shuffle(all(c));
    int n = sz(c); int m = dp[n][d].se;

    vector<int> nc1,nc2;
    forf(i,0,m-1) nc1.pb(c[i]);
    forf(i,m,n-1) nc2.pb(c[i]);
    for(auto i : nc1) v[i] = 1;
    int f = test_students(v);
    for(auto i : nc1) v[i] = 0;
    if(f){
        go(nc1, 1);
        go(nc2,0);
    }
    else{
        go(nc2,d);
    }
}

std::vector<bool> find_positive() {
    //cout<<dp[N][1].fs;

    forf(i,0,N-1) answer[i] = 0;
    vector<int> c; forf(i,0,N-1) c.push_back(i);
    go(c,0);
    return answer;
}

int main() {
    int T;

    scanf("%d %lf %d", &N, &P, &T);

    // You may perform any extra initialization here.
    answer.resize(N,0);
    v.resize(N,0);
    findn();
    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:42:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   42 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:114:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:132:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  132 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 46.04 / 90