#include <bits/stdc++.h>

using namespace std;
using ll = long long;

void solve() {
    int n;
    cin >> n;
    vector<int> a(n + 1), b(n + 1);
    vector<int> posa(n + 1), posb(n + 1);
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
        posa[a[i]] = i;
    }
    for (int i = 1; i <= n; ++i) {
        cin >> b[i];
        posb[b[i]] = i;
    }

    vector edge(n + 1, vector(n + 1, 0));
    vector<int> vis(n + 1);
    for (int i = 1; i <= n; ++i) {
        int u = i;
        int v = posb[a[i]];
        if (a[u] > a[v]) {
            edge[u][v] = 1;
            edge[v][u] = -1;
        }
        else if (a[u] < a[v]) {
            edge[v][u] = 1;
            edge[u][v] = -1;
        } else {
            vis[a[i]] = 1;
        }
    }



    vector<array<int, 2> > ans;
    int i = n;
    while (true) {
        if (i == 0) break;
//        cerr << i << " \n";
        if (vis[i]) {
            i--;
            continue;
        }
        int u = posa[i];
//        cerr << u << " u\n";
        vector<int> to;
        for (int j = u + 1; j <= n; ++j) {
            if (edge[u][j] == 1) to.emplace_back(j);
        }
        if (to.empty()) {cout << "-1\n"; return;}
        int v = to[0];
        ans.push_back({u, v});
        int lstu = 0, lstv = 0;
        for (int j = 1; j <= n; ++j) {
            if (edge[u][j] != 0 && j != v) {
                lstu = j;
                break;
            }
        }
        for (int j = 1; j <= n; ++j) {
            if (edge[v][j] != 0 && j != u) {
                lstv = j;
                break;
            }
        }
        for (int j = 1; j <= n; ++j) {
            edge[u][j] = edge[j][u] = 0;
            edge[v][j] = edge[j][v] = 0;
        }
        swap(a[u], a[v]);
        posa[a[u]] = u;
        posa[a[v]] = v;
        int lsti = i;
        if (a[u] != b[u]) {
            vis[a[v]] = 1;
            lsti = -1;
            if (a[v] == i) {
                i--;
            }
            if (a[u] > a[lstu]) {
                edge[u][lstu] = 1;
                edge[lstu][u] = -1;
            } else if (a[u] < a[lstu]) {
                edge[lstu][u] = 1;
                edge[u][lstu] = -1;
            } else vis[a[u]] = 1;
            if (a[u] > a[lstv]) {
                edge[u][lstv] = 1;
                edge[lstv][u] = -1;
            } else if (a[u] < a[lstv]) {
                edge[lstv][u] = 1;
                edge[u][lstv] = -1;
            } else vis[a[u]] = 1;
        }
        if (a[v] != b[v]) {
            vis[a[u]] = 1;
            lsti = -1;
            if (a[u] == i) {
                i--;
            }
            if (a[v] > a[lstu]) {
                edge[v][lstu] = 1;
                edge[lstu][v] = -1;
            } else if (a[v] < a[lstu]) {
                edge[lstu][v] = 1;
                edge[v][lstu] = -1;
            } else vis[a[v]] = 1;
            if (a[v] > a[lstv]) {
                edge[v][lstv] = 1;
                edge[lstv][v] = -1;
            } else if (a[v] < a[lstv]) {
                edge[lstv][v] = 1;
                edge[v][lstv] = -1;
            } else vis[a[v]] = 1;
        }
        if (i == lsti) {
            vis[a[u]] = vis[a[v]] = 1;
            i--;
        }
//        for (int k = 1; k <= n; ++k) {
//            for (int j = 1; j <= n; ++j) {
//                cerr << edge[k][j] << " \n"[j == n];
//            }
//        }
//        cerr << '\n';

    }
    cout << ssize(ans) << "\n";
    for (i = 0; i < ssize(ans); ++i) {
        cout << ans[i][0] << " " << ans[i][1] << "\n";
    }
}

int main() {
    cin.tie(nullptr) -> sync_with_stdio(false);

    int _;
    cin >> _;
    while (_--) solve();
    return 0;
}