Submission #1076875

#	Time	Username	Problem	Language	Result	Execution time	Memory
1076875		anton	COVID tests (CEOI24_covid)	C++17	0 / 100	5715 ms	43152 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];

void do_split(int l, int r,vector<bool>& ans){
    if(l==r){
        ans[l] = true;
        return;
    }
    int opti_len = split_len[r-l+1];
    if(test_inter(l, l+opti_len-1)){
        do_split(l, l+opti_len-1, ans);
        if(test_inter(l+opti_len, r)){
            do_split(l+opti_len, r, ans);
        }
    }
    else{
        do_split(l+opti_len, r, ans);
    }
}

int find_first(int l, int r){
    if(l == r){
        return l;
    }
    int opti_len = split_len[r-l+1];
    if(test_inter(l, l+opti_len-1)){
        find_first(l, l+opti_len-1);
    }
    else{
        find_first(l+opti_len, r);
    }
}
std::vector<bool> find_positive() {
    std::vector<bool> answer(N);

   int l = 0;

    while(l<N && test_inter(l, N-1)){
        l = find_first(l, N-1);
        answer[l] = true;
        l++;
    }
    
    /*for(int i = 0; i<N; i+=group_sz){
        vector<bool>cur_mask (N, false);

        vector<int> order;
        for(int j = i; j<min(i+group_sz, N); j++){
            cur_mask[j] = true;
        }    
        
        if(test_students(cur_mask)){
            bool found = false;
            for(int j = i; j<min(i+group_sz, N); j++){
                answer[j] = test_single(j);
                cur_mask[j] = false;
                if(answer[j] && j<min(i+group_sz, N)-1){
                    if(!test_students(cur_mask)){
                        break;
                    }
                }
            }
        }
    }*/


    return answer;
}

int get_sz(double p, double target){
    int res = 1;
    double cur_p = p;
    while(cur_p>0.5){
        res ++;
        cur_p*=p;
    }
    return res;
}

double at_least_1(int len){
    return 1.-pow(1.-P, len);
}
int main() {
    int T;
    scanf("%d %lf %d", &N, &P, &T);

    // You may perform any extra initialization here.
    group_sz= min(max(get_sz((1.-P), 0.5), 1), N/2);

    vector<double> expected_turns(N+1, 1e18);
    for(int i = 1; i<=N; i++){
        if(i==1){
            expected_turns[i] = 0.;
        }
        else{
            for(int j = 1; j<i; j++){
                double total = at_least_1(j) * pow(1.-P, i-j) + at_least_1(i-j) * pow(1.-P, j) +at_least_1(j)*at_least_1(i-j);
                double prop_j = (at_least_1(j) * pow(1.-P, i-j) + at_least_1(j)*at_least_1(i-j))/total;
                double prop_both = (at_least_1(j)*at_least_1(i-j))/total;
                double prop_i = (at_least_1(i-j) * pow(1.-P, j) + at_least_1(j)*at_least_1(i-j))/total;
                double other = 1.+ prop_j*expected_turns[j] +prop_i*expected_turns[i-j];
                if(other< expected_turns[i]){
                    split_len[i] = j;
                    expected_turns[i]= other;
                }
            
            }
        }
    }
    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 'int main()':
Main.cpp:149:24: warning: unused variable 'prop_both' [-Wunused-variable]
  149 |                 double prop_both = (at_least_1(j)*at_least_1(i-j))/total;
      |                        ^~~~~~~~~
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 find_first(int, int)':
Main.cpp:82:1: warning: control reaches end of non-void function [-Wreturn-type]
   82 | }
      | ^
Main.cpp: In function 'int main()':
Main.cpp:135:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  135 |     scanf("%d %lf %d", &N, &P, &T);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:172:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  172 |         scanf(" %c", &verdict);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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