bzoj 2060: [Usaco2010 Nov] Visiting Cows Visiting Cows【Tree DP】

Let f[u][0/1] be the point u is not selected/selected, and transfer from the son when transferring, f[u][1]=sum(f[son][0])+1, f[u] ][0]=sum(max(f[son][0],f[e[i].to][1]))

#include<iostream>
#include<cstdio>
using namespace std;
const int N=50005;
int n,h[N],cnt,f[N][2];
struct qwe
{
    int ne,to;
}e[N<<1];
int read()
{
    int r=0,f=1;
    char p=getchar();
    while(p>'9'||p<'0')
    {
        if(p=='-')
            f=-1;
        p=getchar();
    }
    while(p>='0'&&p<='9')
    {
        r=r*10+p-48;
        p=getchar();
    }
    return r*f;
}
void add(int u,int v)
{
    cnt++;
    e[cnt].ne=h[u];
    e[cnt].to=v;
    h[u]=cnt;
}
void dfs(int u,int fa)
{
    int s0=0,s1=0;
    for(int i=h[u];i;i=e[i].ne)
        if(e[i].to!=fa)
        {
            dfs(e[i].to,u);
            s0+=f[e[i].to][0];
            s1+=max(f[e[i].to][0],f[e[i].to][1]);
        }
    f[u][0]=s1;
    f[u][1]=s0+1;
}
int main()
{
    n=read();
    for(int i=1;i<n;i++)
    {
        int x=read(),y=read();
        add(x,y),add(y,x);
    }
    dfs(1,0);
    printf("%d\n",max(f[1][0],f[1][1]));
    return 0;
}