[HNOI2003]消防局的设立

题目传送门

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define re register
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define P pair<int,int>
const int N=1e4;
const int mod=1e9+7;
void read(int &a)
{
    a=0;
    int d=1;
    char ch;
    while(ch=getchar(),ch>'9'||ch<'0')
        if(ch=='-')
            d=-1;
    a=ch-'0';
    while(ch=getchar(),ch>='0'&&ch<='9')
        a=a*10+ch-'0';
    a*=d;
}
void write(int x)
{
    if(x<0)
        putchar(45),x=-x;
    if(x>9)
        write(x/10);
    putchar(x%10+'0');
}
int dep[1005],f[1005],d[1005],a[1005];
bool cmp(int x,int y)
{
    return dep[x]>dep[y];
}
int main()
{
    int n;
    read(n);
    d[0]=d[1]=N;
    a[1]=1;
    for(re int i=2;i<=n;i++)
    {
        read(f[i]);
        d[i]=N;
        dep[i]=dep[f[i]]+1;
        a[i]=i;
    }
    sort(a+1,a+n+1,cmp);
    int ans=0;
    for(re int i=1;i<=n;i++)
    {
        int u=a[i];
        int v=f[u];
        int w=f[v];
        d[u]=min(d[u],min(d[v]+1,d[w]+2));
        if(d[u]>2)
        {
            d[w]=0;///在最底层上两个建，贪心。
            ans++;
            d[f[w]]=min(d[f[w]],1);///更新在这个消防站的上两个点
            d[f[f[w]]]=min(d[f[f[w]]],2);
        }
    }
    write(ans);
    return 0;
}