Codeforces Round #321 (Div. 2) C. Kefa and Park time limit per test

C. Kefa and Park

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Kefa decided to celebrate his first big salary by going to the restaurant.

He lives by an unusual park. The park is a rooted tree consisting of n vertices with the root at vertex 1. Vertex 1 also contains Kefa's house. Unfortunaely for our hero, the park also contains cats. Kefa has already found out what are the vertices with cats in them.

The leaf vertices of the park contain restaurants. Kefa wants to choose a restaurant where he will go, but unfortunately he is very afraid of cats, so there is no way he will go to the restaurant if the path from the restaurant to his house contains more than m consecutive vertices with cats.

Your task is to help Kefa count the number of restaurants where he can go.

Input

The first line contains two integers, n and m (2 ≤ n ≤ 10⁵, 1 ≤ m ≤ n) — the number of vertices of the tree and the maximum number of consecutive vertices with cats that is still ok for Kefa.

The second line contains n integers a₁, a₂, ..., a_n, where each a_i either equals to 0 (then vertex i has no cat), or equals to 1 (then vertex i has a cat).

Next n - 1 lines contains the edges of the tree in the format "x_i y_i" (without the quotes) (1 ≤ x_i, y_i ≤ n, x_i ≠ y_i), where x_i and y_i are the vertices of the tree, connected by an edge.

It is guaranteed that the given set of edges specifies a tree.

Output

A single integer — the number of distinct leaves of a tree the path to which from Kefa's home contains at most m consecutive vertices with cats.

Sample test(s)

Input

4 1
1 1 0 0
1 2
1 3
1 4

Output

2

Input

7 1
1 0 1 1 0 0 0
1 2
1 3
2 4
2 5
3 6
3 7

Output

2

Note

Let us remind you that a tree is a connected graph on n vertices and n - 1 edge. A rooted tree is a tree with a special vertex called root. In a rooted tree among any two vertices connected by an edge, one vertex is a parent (the one closer to the root), and the other one is a child. A vertex is called a leaf, if it has no children.

Note to the first sample test: The vertices containing cats are marked red. The restaurants are at vertices 2, 3, 4. Kefa can't go only to the restaurant located at vertex 2.

Note to the second sample test: The restaurants are located at vertices 4, 5, 6, 7. Kefa can't go to restaurants 6, 7.

题目大意：一棵树，有的节点上有猫，有的没有。求出从根节点出发，到达叶子节点的路径中连续出现猫的数量不能超过m的路径有几条。

解题思路：DFS。细节：vector构造树时因为不知道谁是父亲节点谁是子节点，因此两个点都当做父亲节点处理。判断叶子节点时，儿子个数为1的就是叶子节点。

代码如下：

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <cmath>
#define ll long long
using namespace std;
const int maxn=100005;
int a[maxn],ans,sum,m;
int vis[maxn];
vector <int> v[maxn];
void dfs(int x,int cnt)
{
	if(cnt>m)
		return;
	int len=v[x].size();
	if(len==1 && x!=1)
	{
		if(a[x])
			cnt++;
		if(cnt>m)
			return;
		ans++;
		return ;
	}
	for(int i=0;i<len;i++)
	{
		if(vis[v[x][i]])
			continue;
		else
			vis[v[x][i]]=1;
		if(a[x])
			dfs(v[x][i],cnt+1);
		else
			dfs(v[x][i],0);
	}
}
int main(void)
{
	int n,x,y;
	ans=0,sum=0;
	memset(vis,0,sizeof(vis));
	scanf("%d%d",&n,&m);
	vis[1]=1;
	for(int i=1;i<=n;i++)
		scanf("%d",&a[i]);
	for(int i=0;i<n-1;i++)
	{
		scanf("%d%d",&x,&y);
		v[x].push_back(y);
		v[y].push_back(x);
	}
	dfs(1,0);
	printf("%d\n",ans);
}