Submission #1077598

#	Time	Username	Problem	Language	Result	Execution time	Memory
1077598		Arturgo	COVID tests (CEOI24_covid)	C++14	100 / 100	3197 ms	8524 KiB

Main

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

int N;
double P;

bool test_students(vector<bool> mask);

bool estPasse[1001][1001];
double dp[1001][1001];

double powers[1001];

double esp(int prefix, int total) {
    if(estPasse[prefix][total]) return dp[prefix][total];
    estPasse[prefix][total] = true;
    
    if(total == 0) return dp[prefix][total] = 0;

    if(prefix == 0) {
        double min_esp = INFINITY;
        for(int sz = 1;sz <= total;sz++) {
            double P_vide = powers[sz];
            min_esp = min(min_esp, 
                1 
                + esp(0, total - sz) * P_vide
                + esp(sz, total) * (1 - P_vide)
            );
        }
        return dp[prefix][total] = min_esp;
    } else if(prefix == 1) {
        return dp[prefix][total] = esp(0, total - 1);
    } else {
        double min_esp = INFINITY;
        for(int sz = 1;sz < prefix;sz++) {
            double P_vide = powers[sz] * (1 - powers[prefix - sz]) / (1 - powers[prefix]);

            min_esp = min(min_esp,
                1
                + esp(prefix - sz, total - sz) * P_vide
                + esp(sz, total) * (1 - P_vide)
            );
        }
        return dp[prefix][total] = min_esp;
    }
}

bool ask_inter(int deb, int fin) {
    vector<bool> mask(N, false);
    fill(mask.begin() + deb, mask.begin() + fin, true);
    return test_students(mask);
}

vector<bool> find_positive() {
    vector<bool> answer(N, false);
    int prefix = 0, total = N;

    while(total != 0) {
        if(prefix == 0) {
            double min_esp = INFINITY;
            int opt_sz = -1;

            for(int sz = 1;sz <= total;sz++) {
                double P_vide = powers[sz];
                double E = 
                    1 
                    + esp(0, total - sz) * P_vide
                    + esp(sz, total) * (1 - P_vide);
                
                if(E < min_esp) {
                    min_esp = E;
                    opt_sz = sz;
                }
            }

            bool ans = ask_inter(N - total, N - total + opt_sz);
            if(ans) {
                prefix = opt_sz;
            } else total -= opt_sz;
        } else if(prefix == 1) {
            answer[N - total] = true;
            prefix = 0;
            total -= 1;
        } else {
            double min_esp = INFINITY;
            int opt_sz = -1;

            for(int sz = 1;sz < prefix;sz++) {
                double P_vide = powers[sz] * (1 - powers[prefix - sz]) / (1 - powers[prefix]);
                double E = 
                    1
                    + esp(prefix - sz, total - sz) * P_vide
                    + esp(sz, total) * (1 - P_vide);
                
                if(E < min_esp) {
                    min_esp = E;
                    opt_sz = sz;
                }
            }

            bool ans = ask_inter(N - total, N - total + opt_sz);
            if(ans) {
                prefix = opt_sz;
            } else {
                prefix -= opt_sz;
                total -= opt_sz;
            }
        }
    }

    return answer;
}

void init() {
    powers[0] = 1.;
    for(int i = 1;i <= 1000;i++) {
        powers[i] = (1 - P) * powers[i - 1];
    }
}

/*
int __nbTests = 0;
vector<bool> __covid;

int main() {
    N = 1000;
    P = 0.2;
    int T = 10;

    init();
    cerr << "ESP: " << esp(0, N) << endl;

    for(int i = 0;i < T;i++) {
        __nbTests = 0;
        __covid.clear();
        for(int i = 0;i < N;i++) {
            __covid.push_back(rand() <= P * RAND_MAX);
        }

        vector<bool> answer = find_positive();
        assert(answer == __covid);

        cerr << i << ": " << __nbTests << endl;
    }
}

bool test_students(vector<bool> mask) {
    __nbTests++;
    bool ok = false;
    for(int i = 0;i < N;i++) {
        if(mask[i] && __covid[i]) ok = true;
    }
    return ok;
}

/*/

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

    init();

    for (int i = 0; i < T; i++) {
        vector<bool> answer = find_positive();
        assert(answer.size() == (size_t)N);

        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;
}

bool test_students(vector<bool> mask) {
    assert(mask.size() == (size_t)N);

    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';
}
//*/

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:160:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  160 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:176:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  176 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp: In function 'bool test_students(std::vector<bool>)':
Main.cpp:195:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  195 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~

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