Submission #1078248

#	Time	Username	Problem	Language	Result	Execution time	Memory
1078248		anton	COVID tests (CEOI24_covid)	C++17	100 / 100	2067 ms	11344 KiB

Main

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

/// You may use:

// The number of students
int N;

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

int group_sz =1;
// 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.
bool test_single(int u){
    vector<bool> mask(N, false);
    mask[u] = true;
    return test_students(mask);
}

bool test_inter(int l, int r){
    vector<bool> mask(N, false);
    for(int i = l; i<=r; i++){
        mask[i] = true;
    }
    return test_students(mask);
}

int split_len[1001][1001];
double expected_turns[1001][1001];
std::vector<bool> find_positive() {
    std::vector<bool> answer(N);

    int total = N;
    int pref = 0;
    while(total>0){
        if(split_len[total][pref] == 0){
            answer[N-total] = true;
            total --;
            pref = 0;
        }
        else{
            int len = split_len[total][pref];
            bool is_one = test_inter(N-total, N-total+len-1);
            if(is_one){
                pref = len;
            }
            else{
                total-=len;

                if(len<pref){
                    pref-=len;
                }
            }
        }
    }
    
    return answer;
}
double memo[1001];

double mpow(int deg){
    return memo[deg];
}
double P_1(int len){
    return 1.-mpow(len);
}
double P_none(int len){
    return mpow(len);
}

void chmax(int total, int pref, int test_len, double expected){
    if(expected_turns[total][pref]>expected){
        split_len[total][pref] = test_len;
        expected_turns[total][pref] = expected;
    }
}
int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);

    memo[0] =1.;
    for(int i =1; i<1001; i++){
        memo[i] = memo[i-1] * (1.-P);
    }
    // You may perform any extra initialization here.
    
    for(int total = 0; total<=N; total++){
        for(int pref=  0; pref<=total; pref++){
            expected_turns[total][pref] = 1e18;
        }
    }

    expected_turns[0][0] = 0.;
    for(int total = 1; total<=N; total++){
        for(int pref=  1; pref<=total; pref++){
            if(pref==1){
                chmax(total, pref, 0, expected_turns[total-1][0]);
            }
            else{
                for(int test_len = 1; test_len<pref; test_len++){
                    double p_cur = P_1(pref);
                    double P_left = P_1(test_len)/p_cur;
                    double expected = P_left * expected_turns[total][test_len] +(1-P_left) * expected_turns[total-test_len][pref-test_len] + 1.;
                    chmax(total, pref, test_len, expected);
                }
            }
        }
        for(int test_len = 1; test_len<=total; test_len++){
            double expected=  P_1(test_len) * expected_turns[total][test_len] + P_none(test_len) * expected_turns[total-test_len][0] + 1.;
            chmax(total, 0, test_len, expected);
        }
    }
    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:28:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |     scanf(" %c", &answer);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp: In function 'int main()':
Main.cpp:103:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  103 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:149:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  149 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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