Perfect Service UVA - 1218

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<sstream>
#include<algorithm>
#include<queue>
#include<deque>
#include<iomanip>
#include<vector>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<functional>
#include<fstream>
#include<memory>
#include<list>
#include<string>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;

#define N 31
#define MAXN 20000 + 9
#define INF 1000000009
#define eps 0.00000001
#define sf(a) scanf("%d",&a)

/*
N台电脑构成树！
选点做服务器，最小支配集！
注意这里每个电脑只能从一台服务器上获得信息，说明不能有一个点和两个支配集的点相连！
所以dp[u][1]的状态就是不可行的！
*/
struct edge
{
int to, next;
}E[MAXN*2];
int head[MAXN];
int cnt, n, dp[MAXN][3];
void init()
{
cnt = 0;
memset(dp, 0, sizeof(dp));
memset(head, -1, sizeof(head));
}
void addedge(int u, int v)
{
E[cnt].to = v;
E[cnt].next = head[u];
head[u] = cnt++;
}
void Dp(int u, int p)
{
dp[u][0] = 1;
dp[u][2] = 0;
bool f = false;
int sum = 0, inc = INF;
for (int i = head[u]; i != -1; i = E[i].next)
{
int v = E[i].to;
if (v == p)
continue;
Dp(v, u);
dp[u][0] += min(dp[v][0], dp[v][2]);
if (dp[v][0] < dp[v][1])
{
f = true;
sum += dp[v][0];
}
else
{
inc = min(inc, dp[v][0] - dp[v][1]);
sum += dp[v][1];
}
if (dp[v][1] != INF&&dp[u][2] != INF)
dp[u][2] += dp[v][1];
else
dp[u][2] = INF;
}
if (inc == INF && !f)
dp[u][1] = INF;
else
{
dp[u][1] = sum;
if (!f) dp[u][1] += inc;
}
}
int main()
{
while (scanf("%d", &n) != EOF)
{
int f, t;
init();
for (int i = 0; i < n - 1; i++)
{
scanf("%d%d", &f, &t);
addedge(f, t);
addedge(t, f);
}
Dp(1, -1);
printf("%d\n", min(dp[1][1], dp[1][0]));
int flag;
scanf("%d", &flag);
if (flag == -1)
break;
}
}