Codeforces 1133F1

题目链接

http://codeforces.com/contest/1133/problem/F1

题意

给一个由$n$个顶点和$m$条边组成的无向未加权连通图，保证没有环和平行边。

求一棵生成树，使得所有顶点的最大度数最大。

思路

1. 找到度数最大的结点
2. 从这个点开始做一次BFS

AC代码

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>
#include<set>
#include<string>
#include<sstream>
#include<cctype>
#include<map>
#include<stack>
#include<queue>
#include<list>
#include<cstdlib>
#include<ctime>
using namespace std;
typedef long long ll;
const double PI = atan(1.0)*4;
const int INF = 0x7ffffff;
const ll MOD = 1000000007;
const int maxn = 200010;
int gcd(int a, int b){return b==0?a:gcd(b,a%b);}

struct Node
{
	vector<int> v;
	int num = 0;
}node[maxn];
int n, m, x, y, root, cnt = 0;
int vis[maxn];

void bfs()
{
	queue<int> q;
	vis[root] = 1;
	q.push(root);
	while(!q.empty())
	{
		int u = q.front();
		q.pop();
		int len = node[u].num;
		for(int i = 0; i < len; i++)
		{
			if(vis[node[u].v[i]] == 0)
			{
				vis[node[u].v[i]] = 1;
				printf("%d %d\n", u, node[u].v[i]);
				q.push(node[u].v[i]);
			}
		}
	}
}

int main()
{
//	freopen("input.txt", "r", stdin);
//  freopen("output.txt", "w", stdout);
	scanf("%d%d", &n, &m);
	for(int i = 0; i < m; i++)
	{
		scanf("%d%d", &x, &y);
		node[x].v.push_back(y);
		node[y].v.push_back(x);
		node[x].num++;
		node[y].num++;
	}
	for(int i = 1; i <= n; i++)
	{
		if(node[i].num > cnt)
		{
			cnt = node[i].num;
			root = i;
		}
	}
	bfs();
	return 0;
}