题解 爆零

传送门

原题，dfs即可

Code:

#include <bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define N 1000010
#define ll long long
#define reg register int
#define fir first
#define sec second
#define make make_pair
#define pb push_back
//#define int long long 

char buf[1<<21], *p1=buf, *p2=buf;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf, 1, 1<<21, stdin)), p1==p2?EOF:*p1++)
inline int read() {
	int ans=0, f=1; char c=getchar();
	while (!isdigit(c)) {if (c=='-') f=-f; c=getchar();}
	while (isdigit(c)) {ans=(ans<<3)+(ans<<1)+(c^48); c=getchar();}
	return ans*f;
}

int n;
int head[N], size;
struct edge{int to, next;}e[N<<1];
inline void add(int s, int t) {e[++size].to=t; e[size].next=head[s]; head[s]=size;}

namespace task1{
	int dep[N], ans, dis, mdep[N];
	vector< pair<int, int> > son[N];
	void dfs1(int u) {
		mdep[u]=dep[u];
		for (int i=head[u],v; ~i; i=e[i].next) {
			v = e[i].to;
			dep[v]=dep[u]+1;
			dfs1(v);
			mdep[u]=max(mdep[u], mdep[v]);
			son[u].pb(make(mdep[v], v));
		}
		sort(son[u].begin(), son[u].end());
		// cout<<"son: "<<u<<' '; for (auto it:son[u]) cout<<it.fir<<','<<it.sec<<' '; cout<<endl;
	}
	void dfs2(int u) {
		ans+=min(dis, dep[u]-1);
		dis=0;
		for (auto v:son[u]) {
			++dis;
			dfs2(v.sec);
			++dis;
		}
	}
	void solve() {
		dep[1]=1; dfs1(1);
		dfs2(1);
		printf("%d\n", ans);
		exit(0);
	}
}

signed main()
{
    freopen("a.in", "r", stdin);
    freopen("a.out", "w", stdout);

	memset(head, -1, sizeof(head));
	n=read();
	for (int i=2; i<=n; ++i) add(read(), i);
	task1::solve();

	return 0;
}