洛谷 2279 [HNOI2003] 消防局的设立 贪心+dfs

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

贪心即可;

#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;}