codeforces 1364D Ehabs Last Corollary

题意:n个点的联通图,一定能找到小于k的环或(k+1)/2个互不相邻点 

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

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int n, m, k;
    std::cin >> n >> m >> k;
	vector<vector<int>> e(n + 1);
	for(int i=0;i<m;i++)
	{
		int x,y;
		cin>>x>>y;
		e[x].push_back(y);
		e[y].push_back(x);
	}
	vector<int>dep(n+1,-1), fa(n+1,-1);
	function <void(int,int)> dfs = [&](int u, int p) 
	{
		for(auto v:e[u])
		{
			if(v == p)continue;
			if(dep[v] == -1) 
			{
				dep[v] = dep[u] + 1;
				fa[v] = u;
				dfs(v,u);
			}
			else if(dep[v] < dep[u] && dep[u]-dep[v] <= k -1) 
			{
				cout<<2<<endl;
				cout<<dep[u]-dep[v]+1<<endl;
				for(int i=u;i!=fa[v];i=fa[i])
				{
					cout<<i<<" ";
				}
				cout<<endl;
				exit(0);
			}
		}
	};
	dep[1] = 0;
	dfs(1,-1);
	vector<int> c;
	int l = (k+1)/2;
	if(n - 1 == m)
	{
		for(int x=0;x<2;x++)
		{
			c.clear();
			for(int i=1;i<=n;i++)
			{
				if((dep[i]&1)==x&&c.size()<l)
				{
					c.push_back(i);
				}
			}
			if(c.size()==l)break;
		}
	}
	else 
	{
		int u=1;
		while(dep[u] < 2*l -2) ++u;
		for(int i=0;i<l;i++,u=fa[fa[u]])
		{
			c.push_back(u);
		}
	}
	cout<< 1 << "\n";
	for(auto x:c)cout<<x<<" ";
	cout<<endl;
    return 0;
}