E被卡常求助

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const int N = 1e6 + 10;
int a[N], b[N], cnt[N], use[N];
vector<pair<int, int>>e[N];
pair<int, int> fangxiang[N];
vector<int>ans;
void dfs(int u){
    for (auto [v, id] : e[u]){
        if (use[id])continue;
        use[id] = 1;
        fangxiang[id] = {u, v};
        dfs(v);
    }
}
void run(){
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)cin >> a[i];
    for (int i = 1; i <= n; i++)cin >> b[i];
    // for (int i = 1; i <= 5; i++)
    //     cout << cnt[i] << " \n"[i == 5];
    for (int i = 1; i <= n; i++){
        cnt[a[i]]++;
    }
    // for (int i = 1; i <= 5; i++)
    //     cout << cnt[i] << " \n"[i == 5];
    for (int i = 1; i <= n; i++){
        cnt[b[i]]++;
    }
    // for (int i = 1; i <= 5; i++)
    //     cout << cnt[i] << " \n"[i == 5];
    for (int i = 1; i <= n; i++)
        if (cnt[i] & 1){
            cout << -1 << endl;
            for (int j = 1; j <= n; j++)
                cnt[j] = 0;
            return;
        }
    for (int i = 1; i <= n; i++){
        int u = a[i], v = b[i];
        e[u].push_back({v, i});
        e[v].push_back({u, i});
    }
    for (int i = 1; i <= n; i++)
        dfs(i);
    for (int i = 1; i <= n; i++)
        if (fangxiang[i].first != a[i])
            ans.push_back(i);
    cout << ans.size() << endl;
    for (int i : ans)cout << i << ' ';
    cout << endl;
    //init
    for (int i = 1; i <= n; i++){
        e[i].clear();
        use[i] = cnt[i] = 0;
    }
    ans.clear();
}
int main(){
    // freopen(".in", "r", stdin);
    // freopen(".out", "w", stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--)run();
    return 0;
}