BZOJ 2060: [Usaco2010 Nov]Visiting Cows 拜访奶牛 树形DP

Code:

#include <bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 200000
using namespace std;
int edges;
int f[maxn],g[maxn];
int hd[maxn],to[maxn],nex[maxn];
void addedge(int u,int v)
{
	nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;
}
void dfs(int u,int fa)
{
	f[u]=1,g[u]=0;
	for(int i=hd[u];i;i=nex[i])
	{
		int v=to[i];
		if(v==fa) continue;
		dfs(v,u);
		f[u]+=g[v];
		g[u]+=max(g[v], f[v]);
	}
}
int main()
{
	// setIO("input");
	int n;
	scanf("%d",&n);
	for(int i=1;i<n;++i)
	{
		int x,y;
		scanf("%d%d",&x,&y);
		addedge(x,y), addedge(y,x);
	}
	dfs(1,0);
	printf("%d\n",max(f[1],g[1]));
	return 0;
}