Submission #1005789

#	Time	Username	Problem	Language	Result	Execution time	Memory
1005789		thinknoexit	Counting Mushrooms (IOI20_mushrooms)	C++17	53.81 / 100	7 ms	600 KiB

mushrooms

#include "mushrooms.h"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int n;
int count_mushrooms(int N) {
	n = N;
	if (n <= 451) {
		int ans = 1;
		for (int i = 2;i < n;i += 2) {
			int v = use_machine({ i - 1, 0, i });
			if (v == 1) ans++;
			else if (v == 0) ans += 2;
		}
		if ((n - 1) & 1) {
			if (!use_machine({ 0, n - 1 })) ans++;
		}
		return ans;
	}
	int sq = sqrt(n);
	vector<int> A, B;
	vector<int> P(n - 1);
	iota(P.begin(), P.end(), 1);
	random_shuffle(P.begin(), P.end());
	A.push_back(0);
	int p;
	for (p = 2;p < n && (int)A.size() < sq && (int)B.size() < sq;p += 2) {
		int v = use_machine({ P[p - 1], 0, P[p - 2] });
		if (v == 0) {
			A.push_back(P[p - 1]);
			A.push_back(P[p - 2]);
		}
		else if (v == 2) {
			B.push_back(P[p - 1]);
			B.push_back(P[p - 2]);
		}
		else {
			if (use_machine({ 0, P[p - 1] })) B.push_back(P[p - 1]), A.push_back(P[p - 2]);
			else B.push_back(P[p - 2]), A.push_back(P[p - 1]);
		}
	}
	p--;
	// count A from p -> n - 1
	int ans = A.size();
	if (A.size() > B.size()) {
		int sz = A.size();
		for (int i = p, j;i < n;i = j) {
			vector<int> Q;
			for (j = i;j < min(n, i + sz - 1);j++) {
				Q.push_back(P[j - 1]);
				Q.push_back(A[j - i]);
			}
			int v = use_machine(Q);
			int s = Q.size();
			ans += (s - v) / 2;
		}
	}
	else {
		int sz = B.size();
		for (int i = p, j;i < n;i = j) {
			vector<int> Q;
			for (j = i;j < min(n, i + sz - 1);j++) {
				Q.push_back(P[j - 1]);
				Q.push_back(B[j - i]);
			}
			int v = use_machine(Q);
			ans += (v + 1) / 2;
		}
	}
	return ans;
}

• Subtask 1: 53.8095 / 100