Codeforces 1364 D

https://codeforc.es/contest/1364/problem/D

 

看错题了，要求小于等于k的环或者（k+1）/2个独立集

找环dfs树就行了，独立集不知道定理，就盲找了，前十几个数字总有在最大独立集中参与的吧...所以就和1相连的所有点都猜一猜。。。。

#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
#include<stack>
using namespace std;
typedef long long ll;
const int maxn = 2e5 + 111;
vector<int>G[maxn], ins[maxn];
stack<int>s;

void add(int x, int y) {
	G[x].push_back(y);
}
int dep[maxn];
int de[maxn];
int n, k, m;
int f = 0;

int root = 0;
int dfs(int x, int fa,int d) {
	if (f) return 0;
	if (dep[x]) return 0;
	dep[x] = d;
	s.push(x);
	if (de[x] == 1) root = x;

	for (int p : G[x]) {
		if (p == fa || f == 1) continue;
		if (dep[p]) {
			int ans = dep[x] - dep[p] + 1;
			
			if (ans <= k && f == 0 && ans > 0) {
				f = 1;
				cout << 2 << endl;
				cout << ans << endl;

				while (s.top() != p && s.size()) {
					cout << s.top() << " ";
					s.pop();
				}
				cout << p << " ";
				cout << endl;
				return 0;
			}
		}
		else if (dep[p] == 0 && f == 0) {
			dfs(p, x, d + 1);
		}
	}
	if(s.size()>0) s.pop();
	return 0;
}
int vis[maxn];
int list[maxn];

int jude(int x) {
	for (int p : G[x]) {
		if (list[p]) return 0;
	}
	return 1;
}
int dfs2(int x,int f) {
	if (vis[x]) return 0;
	vis[x] = 1;

	if (jude(x)) {
		ins[f].push_back(x);
		list[x] = 1;
	}
	for (int p : G[x]) {
		dfs2(p, f);
	}
	return 0;
}
vector<int>cn;
int main() {
	
	cin >> n >> m >> k;
	int len = (k + 1) / 2;
	
	for (int i = 0; i < m; i++) {
		int x, y;
		cin >> x >> y;
		add(x, y);
		add(y, x);
		de[x]++;
		de[y]++;
    }
	dfs(1, -1, 1);
	//memset(vis, 0, sizeof(vis));
	if (!f) {
		for (int i = 1; i <= 10; i++) {
			cn.push_back(i);
			for (int p : G[i]) {
				cn.push_back(p);
				if (cn.size() >= 10) break;
			}
			if (cn.size() >= 10) break;
		}
		

		for (int i = 0; i < cn.size(); i++) {
			int x = cn[i];
			memset(vis, 0, sizeof(vis));
			memset(list, 0, sizeof(list));
			dfs2(x, i);
		}
		int cnt = 0;
		int len = (k + 1) / 2;
		
		cout << 1 << endl;
		
		for (int i = 0; i < cn.size(); i++) {
			if (ins[i].size() >= (k + 1) / 2) {
				for (int j = 0; j < len; j++){
					cout << ins[i][j] << " ";
				}
				return 0;
			}
		}

	}
	return 0;
}