Submission #1195412

#	Time	Username	Problem	Language	Result	Execution time	Memory
1195412		franuch	COVID tests (CEOI24_covid)	C++20	48.81 / 100	826 ms	708 KiB

Main

#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bits/stdc++.h>
typedef int ll;
typedef long double ld;
using namespace std;
typedef pair<ll, ll> pll;
#define vc vector
const ll INF = 1e6;
vc<ll> bestp, best;

/// 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.
vc<bool> res;
void rec(ll l, ll r, bool pos) {
	ll s = (r - l + 1);
	if (s == 0)
		return;
	if (s == 1 and pos) {
		res[l] = true;
		return;
	}
	if (s == 1) {
		vc<bool> mask(N, false);
		mask[l] = true;
		if (test_students(mask))
			res[l] = true;
		return;
	}
	
	ll d;
	if (pos)
		d = bestp[s];
	else
		d = best[s];

	vc<bool> mask(N, false);
	for (ll i = l; i < l + d; i++)
		mask[i] = true;
	if (test_students(mask)) {
		rec(l, l + d - 1, true);
		pos = false;
	}
	rec(l + d, r, pos);
}

std::vector<bool> find_positive() {
	res.assign(N, false);
	rec(0, N - 1, false);
	return res;
}

void dynamic() {
	vc<ld> exp(N + 1);
	exp[0] = 1;
	for (ll i = 1; i <= N; i++)
		exp[i] = exp[i - 1] * (1 - P);

	vc<ld> dpp(N + 1);
	vc<ld> dp(N + 1);
	dp[0] = dpp[0] = dpp[1] = 0;
	dp[1] = 1;
	best.assign(N + 1, 0);
	bestp.assign(N + 1, 0);
	for (ll i = 2; i <= N; i++) {
		dp[i] = INF;
		dpp[i] = INF;
		for (ll j = 1; j < i; j++) {
			ld x = dp[i - j] + (1 - exp[j]) * dpp[j] + 1;
			ld pp = (1 - exp[j]) / (1 - exp[i]);
			ld xp = pp * dp[i - j] + (1 - pp) * dpp[i - j] + pp * dpp[j] + 1;
			if (x < dp[i]) {
				dp[i] = x;
				best[i] = j;
			}
			if (xp < dpp[i]) {
				dpp[i] = xp;
				bestp[i] = j;
			}
		}
	}
}

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

    // You may perform any extra initialization here.
	dynamic();

    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:37:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:119:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  119 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:136:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  136 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 10 / 10
• Subtask 2: 38.81 / 90