Submission #315444

#	Time	Username	Problem	Language	Result	Execution time	Memory
315444		neizod	Counting Mushrooms (IOI20_mushrooms)	C++17	100 / 100	13 ms	640 KiB

mushrooms

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


bool swapped = false;
int i = 1;
int just_count_A = 0;
int just_count_B = 0;
vector<int> A = { 0 };
vector<int> B = { };
vector<int> I = { };


void shuffled_index(int n) {
    srand(time(0));
    for (int j=0; j<n; j++) {
        I.push_back(j);
    }
    random_shuffle(I.begin()+1, I.end());
}


int calc_pivots_size(int n) {
    return 1.5 + (3*sqrt(n-2)/4);
}


void make_swap() {
    swapped = not swapped;
    swap(just_count_A, just_count_B);
    swap(A, B);
}


bool decide_swap() {
    if (A.size() < B.size()) {
        make_swap();
    }
    return true;
}


int handle_parity(int parity) {
    (parity == 0 ? A : B).push_back(I[i]);
    return 1;
}


int handle_pair(int raw_info) {
    int even024 = raw_info - (raw_info%2);
    if (even024 == 2) {
        throw invalid_argument("conflict: need more info to handle this case");
    }
    (even024 == 0 ? A : B).push_back(I[i]);
    (even024 == 0 ? A : B).push_back(I[i+1]);
    return 2;
}


int handle_conflict_pair(int raw_info) {
    int flag3b = raw_info - 1;
    (flag3b & 0b100 ? A : B).push_back(I[i]);
    (flag3b & 0b100 ? B : A).push_back(I[i+1]);
    (flag3b & 0b010 ? B : A).push_back(I[i+2]);
    (flag3b & 0b001 ? B : A).push_back(I[i+3]);
    return 4;
}


void get_pivots(int n) {
    int info;
    int size = calc_pivots_size(n);
    while (decide_swap() and (int)A.size() < size and i+5 < n) {
        if (A.size() < 2) {
            i += handle_parity(use_machine({ I[i], A[0] }));
        } else if (A.size() < 3 or B.size() < 2) {
            info = use_machine({ I[i], A[0], I[i+1], A[1] });
            i += handle_parity(info%2);
            i += handle_parity(info/2);
        } else {
            info = use_machine({ I[i], A[0], I[i+1], A[1], I[i+2], A[2] });
            i += handle_parity(info%2);
            try {
                i += handle_pair(info);
            } catch (const invalid_argument &) {
                info = use_machine({ B[0], I[i], B[1], A[0], I[i+1], A[1], I[i+2], A[2], I[i+3] });
                i += handle_conflict_pair(info);
            }
        }
    }
}


vector<int> make_sample(int size) {
    vector<int> sample = { };
    for (int j=0; j<size; j++) {
        sample.insert(sample.end(), { I[i+j], A[j] });
    }
    return sample;
}


void count_the_rest(int n) {
    while (decide_swap() and i < n) {
        int test_size = min((int)A.size(), n-i);
        int info = use_machine(make_sample(test_size));
        i += handle_parity(info%2);
        i += test_size-1;
        just_count_A += (test_size-1) - (info/2);
        just_count_B += info/2;
    }
}


int count_mushrooms(int n) {
    shuffled_index(n);
    get_pivots(n);
    count_the_rest(n);
    if (swapped) {
        make_swap();
    }
    return A.size() + just_count_A;
}

• Subtask 1: 100 / 100