codeforces 573C. Bear and Drawing

传送门：http://codeforces.com/problemset/problem/573/c

思路：见官方题解。。。

#include<cstdio>
#include<vector>
#include<cstring>
#include<algorithm>
const int maxn=100010;
using namespace std;
int n,leg[maxn];bool del[maxn];
vector<int> w[maxn];

void dfs(int a,int fa){
	if (w[a].size()<=2){
		del[a]=1;
		for (int i=0;i<w[a].size();i++) 
			if (w[a][i]!=fa) dfs(w[a][i],a); 
	}
}

int main(){
	scanf("%d",&n);
	for (int i=1,a,b;i<n;i++) scanf("%d%d",&a,&b),w[a].push_back(b),w[b].push_back(a);
	for (int i=1;i<=n;i++) if (w[i].size()==1) dfs(i,0);
	for (int i=1;i<=n;i++)
		for (int j=0;j<w[i].size();j++)
			if (del[w[i][j]]) leg[i]++;
	for (int i=1;i<=n;i++)
		if (!del[i]){
			int cnt=0;
			for (int j=0;j<w[i].size();j++){
				int b=w[i][j];
				if (!del[b]&&w[b].size()>min(leg[b],2)+1) cnt++;
			}
			if (cnt>2){puts("No");return 0;}
		}
	puts("Yes");
	return 0;
}