poj 1848 Tree

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<string>
#include<queue>
#include<algorithm>
#include<vector>
#include<stack>
#include<list>
#include<iostream>
#include<map>
using namespace std;
#define inf 0x3f3f3f3f
#define Max 110
int max(int a,int b)
{
return a>b?a:b;
}
int min(int a,int b)
{
return a<b?a:b;
}
struct node
{
int to,next;
}e[2*110];
int p[110],eid,n;
int dp[110][3];
inline void addedge(int u,int v)
{
e[eid].to=v;
e[eid].next=p[u];
p[u]=eid++;
}
void dfs(int u,int pre)
{
int v,sum=0,i,j;
dp[u][0]=dp[u][2]=1000;
for(i=p[u];i!=-1;i=e[i].next)
{
v=e[i].to;
if(v==pre)
continue;
dfs(v,u);
sum+=dp[v][0];
}
dp[u][1]=sum;
for(i=p[u];i!=-1;i=e[i].next)
{
v=e[i].to;
if(v==pre)
continue;
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(j=p[u];j!=-1;j=e[j].next)
{
int v2=e[j].to;
if(i==j||v2==pre)
continue;
dp[u][0]=min(dp[u][0],sum-dp[v][0]-dp[v2][0]+min(dp[v][1],dp[v][2])+min(dp[v2][1],dp[v2][2])+1);
}
}
//  printf("%d %d %d %d\n",u,dp[u][0],dp[u][1],dp[u][2]);
}
int main()
{
int i,j,u,v;
while(scanf("%d",&n)!=EOF)
{
eid=0;
memset(p,-1,sizeof(p));
for(i=1;i<n;i++)
{
scanf("%d%d",&u,&v);
addedge(u,v);
addedge(v,u);
}
dfs(1,0);
if(dp[1][0]>=1000)
printf("-1\n");
else
printf("%d\n",dp[1][0]);
}
}