#include<bits/stdc++.h>
#define nl "\n"
#define fi first
#define se second
#define pi 3.14159
#define ll long long
#define odd(a)  (a&1)
#define even(a)  !(a&1)
#define Mod 1'000'000'007
#define INF 2'000'000'000 // 2e9
#define sz(x) int(x.size())
#define charToInt(s) (s - '0')
#define ull unsigned long long
#define number_line iota(all(vec) , 1)
#define all(s) s.begin(), s.end()
#define rall(v) v.rbegin() , v.rend()
#define fixed(n) fixed << setprecision(n)
#define Num_of_Digits(n) ((int)log10(n) + 1)
#define to_decimal(bin) stoll(bin, nullptr, 2)
#define Ceil(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define Floor(n, m) (((n) / (m)) - ((n) % (m) ? 0 : 1))
#define Upper(s) transform(all(s), s.begin(), ::toupper);
#define Lower(s) transform(all(s), s.begin(), ::tolower);
#define cout_map(mp) for(auto& [f, s] : mp) cout << f << "  " << s << "\n";
//  ----- bits-------
#define pcnt(n) __builtin_popcount(n)
#define pcntll(n) __builtin_popcountll(n)
#define clz(n) __builtin_clz(n)    // <---100
#define clzll(n) __builtin_clzll(n)
#define ctz(n) __builtin_ctz(n)  // 0001---->
#define ctzll(n) __builtin_ctzll(n)

using namespace std;

template < typename T = int > istream& operator >> (istream &in, vector < T > & v){
    for(auto & x : v) in >> x;
    return in;
}

template < typename T = int > ostream& operator << (ostream &out, const vector < T > & v){
    for(const T & x : v) out << x << " ";
    return out;
}

void esraa()
{
    //freopen("shuffle.in", "r", stdin), freopen("shuffle.out", "w", stdout);
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
int n;
vector < vector < int > > adj;
const int N = 2e5 + 10;
set < pair < int , int > > st;
vector < int > color,  sz;
map < int , int > mp;
void dfs(int node , int par = -1){
    sz[node] = 1;
    for(auto & child : adj[node]){
        if(par == child) continue;
        dfs(child , node);
        sz[node] += sz[child];
    }
}

void dfs2(int node , int par = -1){
    for(auto & child : adj[node]){
        if(par == child) continue;
        dfs2(child , node);
        if(sz[child] == n / 2) st.insert({node , child});
    }
}

void dfs3(int node , int par){
    mp[color[node]]++;
    for(auto & child : adj[node]){
        if(par == child) continue;
        dfs3(child , node);
    }
}
void solve(){
    cin >> n;
    adj.assign(n + 5 , vector < int > ());
    st.clear();
    color.assign(n + 5 , 0);
    sz.assign(n + 5 , 0);
    vector < int > freq(n + 5);
    for(int i = 1 ; i <= n ; i++) cin >> color[i] , freq[color[i]]++;

    for(int i = 0 ; i < n - 1 ; i++){
        int u , v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    if(n & 1) return void(cout << -1 << nl);
    for(auto & i : freq) if(i & 1) return void(cout << -1 << nl);

    dfs(1);
    dfs2(1);
    if(st.empty()) return void(cout << -1 << nl);

    int node = st.begin() -> first , par = st.begin() -> second;
    mp.clear();

    dfs3(node , par);
    int res = 0;
    for(int i = 1 ; i <= n ; i++){
        res += abs(freq[i] / 2 - mp[i]);
    }
    cout << res / 2 << nl;



}
int main()
{
    esraa();
    int t = 1;
    cin >> t;
    //cin.ignore();
    while(t--)
      solve();
    return 0;
}