美团2017年CodeM大赛-初赛B轮 黑白树 (树形dp)

#include <iostream>
#include <sstream>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <string.h>
#include <bitset>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl ‘\n‘
#define DB(a) ({REP(__i,1,n) cout<<a[__i]<<‘ ‘;hr;})
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int P = 1e9+7, P2 = 998244353, INF = 0x3f3f3f3f;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
inline int rd() {int x=0;char p=getchar();while(p<‘0‘||p>‘9‘)p=getchar();while(p>=‘0‘&&p<=‘9‘)x=x*10+p-‘0‘,p=getchar();return x;}
//head


const int N = 1e6+10;
int n, ans, fa[N], k[N];
vector<int> g[N];

int dfs(int x) {
	int d = 0;
	for (int y:g[x]) d=max(d,dfs(y));
	k[fa[x]] = max(k[fa[x]], k[x]-1);
	if (d>0) return d-1;
	return ++ans, k[x]-1;
}

int main() {
	scanf("%d", &n);
	REP(i,2,n) {
		scanf("%d", fa+i);
		g[fa[i]].pb(i);
	}
	REP(i,1,n) scanf("%d", k+i);
	dfs(1);
	printf("%d\n", ans);
}