洛谷 2279 [HNOI2003] 消防局的設立 貪心+dfs

題目：
https://www.luogu.org/problemnew/show/2279

貪心即可;

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int MAXN=1000001;

int fst[MAXN],nxt[MAXN],fa[MAXN],deep[MAXN];
struct hh {int from,to;}ma[MAXN];
int n,tot,ans;
bool vis[MAXN];

void build(int f,int t)
{
    ma[++tot]=(hh){f,t};
    nxt[tot]=fst[f];
    fst[f]=tot;
    return;
}

void dfs(int x,int f)
{
    fa[x]=f,deep[x]=deep[f]+1;
    for(int i=fst[x];i;i=nxt[i])
    {
        int v=ma[i].to;
        if(v==f) continue;
        dfs(v,x);
    }
    return;
}

void cut(int x,int depth)
{
    vis[x]=1;
    for(int i=fst[x];i;i=nxt[i])
    {
        int v=ma[i].to;
        if(depth+1<=2)
        cut(v,depth+1);
    }
    return;
}


void calc()
{
    while(1)
    {
        int i=1,Max=0,v=0;
        for(i=1;i<=n;i++)
        {
            if(!vis[i] && deep[i]>Max)
                 Max=deep[i],v=i;
        }
        vis[v]=1;
        if(!v) break;
        cut(fa[fa[v]],0),ans++;
    }
    return;
}

void solve()
{
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
    {
        int x;
        scanf("%d",&x);
        build(x,i),build(i,x);
    }
    dfs(1,1),calc();
    cout<<ans<<endl;
}


int main()
{
    solve();
    return 0;
}