UVA1218 Perfect Service

 1 /*by SilverN*/
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 #include<vector>
 8 #include<queue>
 9 using namespace std;
10 const int mxn=20000;
11 vector<int>e[mxn];
12 int f[mxn][5];
13 int vis[mxn];
14 int n;
15 void dp(int u){
16     int i,j;
17     vis[u]=1;
18     f[u][0]=1;f[u][1]=0;f[u][2]=mxn;
19     queue<int>q;
20     for(i=0;i<e[u].size();i++){
21         int v=e[u][i];
22         if(!vis[v]){
23             dp(v);
24             q.push(v);
25             f[u][0]+=min(f[v][1],f[v][0]);
26             f[u][1]+=f[v][2];
27         }
28     }
29     while(!q.empty()){
30         f[u][2]=min(f[u][2],f[u][1]-f[q.front()][2]+f[q.front()][0]);
31         q.pop();
32     }
33     return;
34 }
35 int main(){ 
36     int i,j;
37     while(scanf("%d",&n) && n!=-1){
38         if(!n)continue;
39         memset(f,0,sizeof f);
40         memset(vis,0,sizeof vis);
41         for(i=1;i<=n;i++) e[i].clear();
42         int x,y;
43         for(i=1;i<n;i++){
44             scanf("%d%d",&x,&y);
45             e[x].push_back(y);
46             e[y].push_back(x);
47         }
48         dp(1);
49         printf("%d\n",min(f[1][0],f[1][2]));
50     }
51     return 0;
52 }