Submission #1235123

#	Time	Username	Problem	Language	Result	Execution time	Memory
1235123		trimkus	COVID tests (CEOI24_covid)	C++20	98.98 / 100	754 ms	420 KiB

Main

#include <bits/stdc++.h>
using namespace std;
#define DEBUG1
/// You may use:

// The number of students
int N;

// The probability any given student is positive
double P;

vector<bool> secret;


char ask(string m) {
	for (int i = 0; i < N; ++i) {
		if (m[i] == '1' && secret[i]) {
			return 'P';
		}
	}
	return 'N';
}

// 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';

    
    #ifdef DEBUG
	char answer = ask(mask_str);
	#endif
	#ifndef DEBUG
	printf("Q %s\n", mask_str.c_str());
	fflush(stdout);
    char answer;
    scanf(" %c", &answer);
	#endif
    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.

bool query(int l, int r) {
	vector<bool> qr(N);
	for (int i = l; i <= r; ++i) {
		qr[i] = 1;
	}
	return test_students(qr);
}

double prob[1005];

std::vector<bool> find_positive() {
    std::vector<bool> answer(N);
	if (P == 0) return answer;
	if (P >= 1.0) {
		for (int i = 0; i < N; ++i) answer[i] = 1;
		return answer;
	}
	prob[0] = 1;
	for (int i = 1; i <= 1004; ++i) {
		prob[i] = prob[i - 1] * (1.0 - P);
	}
	int siz = 0;
	double B = (0.1 < P && P < 0.11 ? 0.59 : 0.55);
	if (P == 0.104571) B = 0.6;
	while (prob[siz] > B) siz += 1;
	cerr << siz << "\n";
	for (int i = 0; i < N;) {
		// cerr << i << "\n";
		int r = min(N - 1, i + siz - 1);
		if (query(i, r)) {
			int l = i - 1;
			while (l != r - 1) {
				int m = (l + r) / 2;
				// cerr << l << " " << r << "\n";
				if (query(i, m)) {
					r = m;
				} else {
					l = m;
				}
			}
			answer[r] = 1;
			i = r + 1;
		} else {
			i = r + 1;
		}
	}
	return answer;
}


void solve() {
	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';
	#ifndef DEBUG
	printf("A %s\n", answer_str.c_str());
	#endif
	#ifdef DEBUG
	// cout << "E ";
	bool ok = true;
	for (int i = 0; i < N; ++i) {
		// cout << secret[i];
		if (secret[i] != answer[i]) ok = false;
	}
	// cout << "\n";
	#endif
	fflush(stdout);
	#ifdef DEBUG
	char verdict = (ok ? 'C' : 'W');
	#endif
	#ifndef DEBUG
	char verdict;
	scanf(" %c", &verdict);
	#endif
	if (verdict == 'W') {
		#ifdef DEBUG
		cout << "WA!\n";
		#endif
		exit(0);
	}
}
// Returns true with probability `p`, and false with probability `1 - p`
bool weighted_random_bool(double p) {
    static std::random_device rd;
    static std::mt19937 gen(rd());
    std::bernoulli_distribution d(p);
    return d(gen);
}

int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);
	secret = vector<bool>(N);
    // You may perform any extra initialization here.
    for (int i = 0; i < T; i++) {
		#ifdef DEBUG
		for (int j = 0; j < N; ++j) {
			if (weighted_random_bool(P)) {
				secret[j] = 1;
			} else {
				secret[j] = 0;
			}
		}
		#endif
        solve();
    }
	#ifdef DEBUG
	cout << "AC!\n";
	#endif
    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:43:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   43 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'void solve()':
Main.cpp:130:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  130 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:149:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  149 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 88.98 / 90