Submission #410992

#	Time	Username	Problem	Language	Result	Execution time	Memory
410992		SeDunion	Counting Mushrooms (IOI20_mushrooms)	C++17	90.76 / 100	12 ms	712 KiB

mushrooms

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

int K;

int askline(int l, int r) {
	vector<int>toquest;
	for (int i = l ; i <= r ; ++ i) toquest.emplace_back(i);
	return use_machine(toquest);
}

using vi = vector<int>;

int count_mushrooms(int n) {
	if (n == 2) {
		return 2 - use_machine({0, 1});
	}
	K = min(n, 100);
	if (K % 2 == 0) K--;
	vector<int>who(n, 2); // 0 -> A, 1 -> B, 2 -> unknown
	who[0] = 0;
	for (int p = 0 ; p < 2 ; ++ p) {
		int ret = use_machine({p, p + 1});
		who[p + 1] = who[p] ^ (ret & 1);
	}
	for (int p = 3 ; p < K - 1 ; p += 2) {
		vector<int>v = (!who[1] ? vi{0, 1} : (who[2] ? vi{1, 2} : vi{0, 2}));
		cerr << p << " " << p + 1 << " as\n";
		int ret = use_machine(vi{p, v[0], p + 1, v[1]});
		who[p] = (who[v[0]] && !(ret & 1)) || (!who[v[0]] && ret & 1);
		who[p + 1] = (who[v[0]] && ret <= 1) || (!who[v[0]] && (ret & 2));
	}
	array<vector<int>, 3>vecs;
	for (int i = 0 ; i < n ; ++ i) {
		vecs[who[i]].emplace_back(i);
	}
	int answer = (int)vecs[0].size();
	for (int i = 0 ; i < (int)vecs[2].size() ;) {
		auto &p = (vecs[0].size() > vecs[1].size() ? vecs[0] : vecs[1]);
		vector<int>ask;
		int l = i, r = min((int)vecs[2].size(), i + (int)p.size()) - 1;
		for (int j = l ; j <= r ; ++ j) {
			ask.emplace_back(vecs[2][j]);
			ask.emplace_back(p[j-l]);
		}
		i = r + 1;
		int ret = use_machine(ask);
		answer += (p == vecs[0] ? r-l+1 - (ret+1)/2 : (ret+1)/2);
		int first = ((p == vecs[0] && ret % 2) || (p == vecs[1] && ret % 2 == 0));
		vecs[first].emplace_back(vecs[2][l]);
	}
	return answer;
}

• Subtask 1: 90.7631 / 100