POJ 3398 Perfect Service(树形DP，最小支配集)

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <set>
#include <stack>
#include <map>
#define LL long long
#define FOR(i, x, y) for(int i=x;i<=y;i++)
using namespace std;
const int MAXN = 11000 + 10;
const int INF = 10000000;
int dp[MAXN][3];
int N;
struct Edge
{
    int to, next;
}edge[MAXN * 2];
int head[MAXN];
int tot = 0;
void addedge(int u, int v)
{
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot++;
}
void init()
{
    memset(head, -1, sizeof(head));
    tot = 0;
    FOR(i, 1, N)
    {
        dp[i][0] = 1;
        dp[i][1] = 0;
        dp[i][2] = INF;
    }
}
void dfs(int u, int pre)
{
    for(int i=head[u]; i!=-1; i=edge[i].next)
    {
        int v = edge[i].to;
        if(v == pre) continue;
        dfs(v, u);
        dp[u][0] += min(dp[v][0], dp[v][1]);
        dp[u][1] += dp[v][2];
        dp[u][2] = min(dp[u][2], dp[v][0] - dp[v][2]);
    }
    dp[u][2] += dp[u][1];
}
int main()
{
    while(scanf("%d", &N)!=EOF)
    {
        if(N == 0) continue;
        if(N == -1) break;
        init();
        int u, v;
        for(int i=1;i<N;i++)
        {
            scanf("%d%d", &u, &v);
            addedge(u, v);
            addedge(v, u);
        }
        dfs(1, 0);
        printf("%d\n", min(dp[1][0], dp[1][2]));
    }
    return 0;
}