大概思路是寻找白点，白点向下看有没有黑点，如果有就需要保留，反之则不需要

#include <bits/stdc++.h>
//#define int long long
using namespace std;
int n;
const int N = 1e5 + 114;
int a[N];
int white[N];
vector<int> v[N];
int cnt;
int ans = 0;
int flag[N];
int FA[N];
int vis[N];
void DFS(int x, int fa){
    FA[x] = fa;
    for(int i = 0;i < v[x].size(); i++){
        if(v[x][i] == fa) continue;
        DFS(v[x][i], x);
    }
}
int dfs(int x, int fa){
    if(vis[x]){
        return flag[x];
    }
    vis[x] = true;
    if(a[x]){
        return flag[x] = true;
    }
    for(int i = 0;i < v[x].size(); i++){
        if(v[x][i] == fa) continue;
        flag[x] = flag[x] | dfs(v[x][i], x);
    }
    return flag[x];
}
signed main()
{
    cin >> n;
    for(int i = 1;i <= n; i++){
        cin >> a[i];
        if(!a[i]){
            white[++cnt] = i;
        }
    }
    for(int i = 1;i <= n - 1; i++){
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    DFS(1, 0);
    for(int i = 1;i <= cnt; i++){
        
        if(dfs(white[i], FA[white[i]])){
            ans ++;
        }
    }
    cout << ans << endl;
    return 0;
}