poj 1848 Tree 树形dp

//poj 1848
//sep9
include <iostream>
#include <vector>
using namespace std;
const int MAXN=128;
const int INF=100000;
vector<int> g[2*MAXN];
int dp[MAXN][3];

void dfs(int u,int p)
{
	vector<int> son;
	int sum=0;
	for(int i=0;i<g[u].size();++i){
		int v=g[u][i];
		if(v!=p){
			dfs(v,u);
			son.push_back(v);
			sum+=dp[v][0];
		}
	}
	if(son.size()==0){
		dp[u][1]=0;
		dp[u][0]=dp[u][2]=INF;
		return ;
	}	
	dp[u][1]=min(INF,sum);
	dp[u][2]=dp[u][0]=INF;
	for(int i=0;i<son.size();++i){
		int v=son[i];
		dp[u][2]=min(dp[u][2],sum-dp[v][0]+min(dp[v][1],dp[v][2]));
		dp[u][0]=min(dp[u][0],sum-dp[v][0]+dp[v][2]+1);
	}
	for(int i=0;i<son.size();++i){
		int v=son[i];
		for(int j=0;j<son.size();++j){
			if(i==j) continue;
			int k=son[j];
			dp[u][0]=min(dp[u][0],sum-dp[v][0]-dp[k][0]+min(dp[v][1],dp[v][2])+min(dp[k][1],dp[k][2])+1);
		}
	}
}

int main()
{
	int n,a,b;
	scanf("%d",&n);
	for(int i=1;i<n;++i){
		scanf("%d%d",&a,&b);
		g[a].push_back(b);
		g[b].push_back(a);
	}	
	dfs(1,-1);
	if(dp[1][0]==INF)
		printf("-1");
	else
		printf("%d",dp[1][0]);
	return 0;	
}