Submission #1134537

#	Time	Username	Problem	Language	Result	Execution time	Memory
1134537		amunduzbaev	COVID tests (CEOI24_covid)	C++20	75.89 / 100	812 ms	412 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>

/// 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:

#include "bits/stdc++.h"

using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

// 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() {
    int n = N;
	
	vector<int> p(n);
	iota(p.begin(), p.end(), 0);
	shuffle(p.begin(), p.end(), rng);
	
	//~ for(auto x : p){
		//~ cout<<x<<" ";
	//~ }
	//~ cout<<"\n";
	
	vector<bool> ans(n, false);
	
	auto find = [&](int l_, int r_){
		for(int i=l_;i<=r_;){
			auto check = [&](int l, int pos){
				vector<bool> mask(n, false);
				
				for(int i=l;i<=pos;i++) mask[p[i]] = true;
				
				bool res = test_students(mask);
				return res;
			};
			if(check(i, r_) == false) break;
			
			int l = i, r = r_;
			while(l < r){
				int m = (l + r) >> 1;
				if(check(i, m)) r = m;
				else l = m + 1;
			}
			
			ans[p[l]] = true;
			i = l + 1;
		}
	};
	
	int B = n;
	if(P >= 0.001) B = 1 / P;
	
	for(int c=0;c * B < n;c++){
		int l_ = c * B, r_ = min(l_ + B, n) - 1;
		
		find(l_, r_);
	}
	
	return ans;
}

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++) {
        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:29:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:96:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   96 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:112:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  112 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 65.89 / 90