牛客-黑白树

https://ac.nowcoder.com/acm/problem/13249

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;
typedef long long ll;
const int maxn = 2e5 + 777;

struct Node {
	int to;
	int nxt;
}G[maxn * 2];

int head[maxn];
int z;
void add(int be, int en) {
	G[++z].to = en;
	G[z].nxt = head[be];
	head[be] = z;
}

ll dp[maxn];//操作了几次
ll list[maxn];
ll ans[maxn];//向上几个祖宗
int de[maxn];
ll cns = 0;
int dfs(int x, int fa) {
	
	for (int i = head[x]; i; i = G[i].nxt) {
		int p = G[i].to;
		if (p == fa) continue;
		dfs(p, x);
		ans[x] = max(ans[p] - 1, ans[x]);
		dp[x] += dp[p];
	} 
	if (ans[x] == 0 ) {
		cns++;
		ans[x] = list[x];
	}
	else {
		list[fa] = max(list[fa], list[x] - 1);
	}
	return 0;
}
int main() {
	int n;
	scanf("%d", &n);
	int be, en;
	for (int i = 2; i <= n; i++) {
		scanf("%d", &be);
		de[be]++;
		de[i]++;
		add(be, i);
		add(i, be);
	}
	for (int i = 1; i <= n; i++) {
		scanf("%lld", &list[i]);
	}

	dfs(1, 0);

	printf("%lld\n", cns);
	return 0;
}