Submission #1256220

#	Time	Username	Problem	Language	Result	Execution time	Memory
1256220		biank	COVID tests (CEOI24_covid)	C++20	100 / 100	2354 ms	15768 KiB

Main

#include "bits/stdc++.h"
using namespace std;

#define forsn(i, s, n) for (int i = int(s); i < int(n); i++)
#define forn(i, n) forsn(i, 0, n)
#define dforsn(i, s, n) for (int i = int(n) - 1; i >= int(s); i--)
#define dforn(i, n) dforsn(i, 0, n)
 
#define sz(x) int(x.size())
#define all(x) begin(x), end(x)
 
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vb = vector<bool>;
using vll = vector<ll>;
using ii = pair<int, int>;
using iii = tuple<int, int, int>;

const int MAX_N = 1005;

/// 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.

ld dp[MAX_N][MAX_N];
int best[MAX_N][MAX_N];

bool test_students(vb 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');
}

map<ii, bool> memo;

bool query(int l, int r) {
    if (r - l == 0) return false;
    if (memo.count(ii{l, r})) return memo[{l, r}];
    vb curr(n, false);
    forsn(i, l, r) curr[i] = true;
    return memo[ii{l, r}] = test_students(curr);
}

vb ret;

const ld INF = 1e9;

void calcDP() {
    if (P == 0) return;
    vector<ld> pot(n + 1);
    pot[0] = 1;
    forsn(i, 1, n + 1) pot[i] = pot[i - 1] * (1 - P);
    dforn(i, n) {
        forsn(j, i + 1, n + 1) {
            if (j - i == 1) dp[i][j] = dp[j][j];
            else {
                dp[i][j] = INF;
                forsn(k, 1, j - i) {
                    ld prob = (1 - pot[k]) / (1 - pot[j - i]);
                    ld curr = prob * dp[i][i + k] + (1 - prob) * dp[i + k][j] + 1;
                    if (dp[i][j] > curr) dp[i][j] = curr, best[i][j] = k;
                }
            }
        }
        dp[i][i] = INF;
        forsn(k, 1, n - i + 1) {
            ld curr = (1 - pot[k]) * dp[i][i + k] + pot[k] * dp[i + k][i + k] + 1;
            if (dp[i][i] > curr) dp[i][i] = curr, best[i][i] = k;
            
        }
    }
}

void solve(int i, int j) {
    if (i == n) return;
    if (j - i == 1) {
        ret[i] = true;
        solve(j, j);
        return; 
    }
    int k = best[i][j];
    if (query(i, i + k)) {
        solve(i, i + k);
    } else {
        solve(i + k, max(j, i + k));
    }
}

vb find_positive() {
    memo.clear();
    ret = vb(n, false);
    if (P != 0) solve(0, 0);
    return ret;
}

int main() {
    
    int T;
    scanf("%d %lf %d", &n, &P, &T);
    
    calcDP();
    
    // 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(vb)':
Main.cpp:48:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:117:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  117 |     scanf("%d %lf %d", &n, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:135:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  135 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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