| # | Time | Username | Problem | Language | Result | Execution time | Memory | 
|---|---|---|---|---|---|---|---|
| 1146475 | crispxx | Binary Subsequences (info1cup17_binary) | C++20 | 0 ms | 0 KiB | 
#include <bits/stdc++.h>
#include "grader.h"
// #include "grader.cpp"
using namespace std;
#define all(x) x.begin(), x.end()
#define pb push_back
#define nl '\n'
int findEgg(int n, vector <pair<int, int>> edges) {
	
	vector<set<int>> adj(n);
	
	for(auto &[u, v] : edges) {
		u--, v--;
		adj[u].emplace(v);
		adj[v].emplace(u);
	}
	
	vector<int> isl;
    
    auto dfs = [&](auto &&dfs, int v, int p) -> void {
		isl.pb(v + 1);
		for(auto to : adj[v]) {
			if(to == p) continue;
			dfs(dfs, to, v);
		}
	};
	
	auto dfs1 = [&](auto &&dfs, int v, int p, vector<vector<int>> &chd) -> void {
		for(auto to : adj[v]) {
			if(to == p) continue;
			
			dfs(dfs, to, v, chd);
			
			for(auto i : chd[to]) chd[v].pb(i);
		}
	};
	
	auto check = [&](int x, int y, int sz) {
		if(x == sz / 2 && y == (sz + 1) / 2) return true;
		if(x == (sz + 1) / 2 && y == sz / 2) return true;
		return false;
	};
	
	vector<int> used(n);
	
	int cur = n;
	
	while(true) {
		
		bool flag = false;
		
		for(auto [u, v] : edges) {
			if(used[u] || used[v]) continue;
			
			adj[u].erase(v);
			adj[v].erase(u);
			
			dfs(dfs, u, -1);
			
			auto isl1 = isl;
			
			isl.clear();
			
			dfs(dfs, v, -1);
			
			auto isl2 = isl;
			
			isl.clear();
			
			int x = isl1.size(), y = isl2.size();
			
			if(check(x, y, cur)) {
				if(query(isl1)) {
					if(x == 1) {
						return isl1[0];
					}
					for(auto i : isl2) {
						used[i - 1] = true;
						cur--;
					}
				} else {
					if(y == 1) {
						return isl2[0];
					}
					for(auto i : isl1) {
						used[i - 1] = true;
						cur--;
					}
				}
				flag = true;
				break;
			}
			
			adj[u].emplace(v);
			adj[v].emplace(u);
		}
		
		if(!flag) {
			for(int r = 0; r < n; r++) {
				
				if(used[r]) continue;
				
				vector <vector<int>> chd(n);
				
				for(int i = 0; i < n; i++) chd[i].pb(i);
				
				dfs1(dfs1, r, -1, chd);
				
				vector<pair<int, int>> tr;
				
				for(auto to : adj[r]) {
					tr.emplace_back(chd[to].size(), to);
				}
				
				sort(all(tr));
				
				vector<int> isl1, isl2;
				
				isl1.pb(r);
				isl2.pb(r);
				
				for(int i = 0; i < (int)tr.size(); i++) {
					auto [sz, v] = tr[i];
					for(auto to : chd[v]) {
						isl1.pb(to);
					}
					int x = isl1.size();
					if(check(x, cur - x + 1, cur + 1)) {
						for(int j = i + 1; j < (int)tr.size(); j++) {
							auto [sz1, v1] = tr[j];
							for(auto to : chd[v1]) isl2.pb(to);
						}
						if(query(isl1)) {
							if((int)isl1.size() == 1) {
								return isl1[0];
							}
							for(auto to : isl2) {
								if(to == r) continue;
								used[to + 1] = 1;
								adj[to].erase(r);
								adj[r].erase(to);
								cur--;
							}
						} else {
							if((int)isl2.size() == 1) {
								return isl2[0];
							}
							for(auto to : isl1) {
								if(to == r) continue;
								used[to + 1] = 1;
								adj[to].erase(r);
								adj[r].erase(to);
								cur--;
							}
						}
						flag = true;
						break;
					}
				}
			}
		}
		
		
		if(!flag) break;
	}
	
	return -1;
}
/**
5
1 2
1 3
2 4
3 5
5
1 2 3 4 5
**/
