Submission #834863

#	Time	Username	Problem	Language	Result	Execution time	Memory
834863		esomer	Rarest Insects (IOI22_insects)	C++17	99.84 / 100	56 ms	432 KiB

insects

#include<bits/stdc++.h>
#include "insects.h"

using namespace std;

mt19937 gen(time(0));

int groups, lft;
vector<bool> done;

int get_groups(int N){
	int groups = 0;
	for(int i = 0; i < N; i++){
		move_inside(i);
		int rep = press_button();
		if(rep > 1) { move_outside(i); }
		else { groups++; done[i] = 1; }
	}
	return groups;
}

int choose_best(int lo, int hi){
	//If I choose mid. Then in the case that all the groups are of size at least mid,
	//I discard (mid - lo + 1) * groups.
	//In the other case, I discard left - chosen (and chosen can be at most (mid - lo + 1) * groups).
	//So I want min((mid - lo + 1) * groups, left - (mid - lo + 1) * groups) to be the maximum.
	int x = lft / 2;
	int bst = x / groups;
	int mn1 = min(bst * groups, lft - bst * groups + 1);
	bst++;
	int mn2 = min(bst * groups, lft - bst * groups + 1);
	if(mn1 < mn2) bst--;
	return max(lo, min(hi, lo + bst - 1));
}

int min_cardinality(int N) {
	done.assign(N, 0);
	int ans = 1;
	groups = get_groups(N);
	lft = N - groups;
	int cnt = groups;
	int lo = 2;
	int hi = N / groups;
	while(lo <= hi && lft > 0) {
		int mid = choose_best(lo, hi);
		vector<int> good, bad;
		vector<int> possible;
		for(int i = 0; i < N; i++) {
			if(!done[i]) possible.push_back(i);
		}
		while((int)possible.size() > 0){
			if((cnt + (int)good.size()) == mid * groups) {
				bad.push_back(possible.back());
				possible.pop_back();
				continue;
			}
			int ind = gen() % ((int)possible.size());
			int i = possible[ind];
			move_inside(i);
			int rep = press_button();
			if(rep > mid) {
				bad.push_back(i);
				move_outside(i);
			} else { good.push_back(i); }
			if(ind != (int)possible.size() - 1) swap(possible[ind], possible[(int)possible.size() - 1]);
			possible.pop_back();
		}
		if((int)good.size() + cnt == mid * groups) {
			ans = mid;
			lo = mid + 1;
			for(int x : good) done[x] = 1;
			cnt += (int)good.size();
			lft -= (int)good.size();
		} else {
			hi = mid - 1;
			for(int x : good) move_outside(x);
			for(int x : bad) done[x] = 1;
			lft -= (int)bad.size();
		}
	}
	return ans;
}

• Subtask 1: 10 / 10
• Subtask 2: 15 / 15
• Subtask 3: 74.84 / 75