#include <bits/stdc++.h> using namespace std; #define print(l) for(auto i:l) cout<<i<<" ";cout<<endl; #define input(t,l,n) vector<t>l(n);for(int i = 0;i<n;i++)cin>>l[i]; #define int long long #define pb push_back #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> #define all(l) l.begin(),l.end() #define pii pair<int,int> #define fi first #define se second const int M = 1e9+7; const int inf = 1e18; int bp(int x, int y, int p){ int res = 1; x = x % p; while (y > 0) { if (y & 1) res = (res * x) % p; y = y >> 1; x = (x * x) % p; } return res; } int MI(int n, int p){ return bp(n, p - 2, p); } int mul(int x,int y, int p){ return x * 1ull * y % p; } int di(int x,int y, int p){ return mul(x, MI(y, p), p); } int n , m , k , q; vector<int>a,b,bad; vector<vector<int>>ansx,ans; map<int,int>done,isbad; void dox(){ // print(bad); for(int i:bad){ if(isbad[i] == 0)continue; if(isbad[b[i]-1] and i != b[i]-1){ isbad[i] = 0; isbad[b[i]-1] = 0; ansx.pb({i,b[i]-1}); // print(a); // print(b); int j = b[i]-1; swap(b[i],a[j]); swap(a[i],b[j]); } } vector<int>lf; for(int i:bad){ if(isbad[i])lf.pb(i); } // print(lf); for(int i = 0;i<lf.size();i+=2){ int ii = lf[i]; int j = lf[i+1]; isbad[ii] = 0; isbad[j] = 0; // cout<<ii<<" "<<j<<endl; ansx.pb({ii,j}); swap(a[ii],b[j]); swap(b[ii],a[j]); } } void solve(int testcase_number){ cin>>n; input(int,A,n); a.clear(); b.clear(); done.clear(); isbad.clear(); for(int i = 0;i<n/2;i++){ a.pb(A[i]); } for(int i = n-1;i>=n/2;i--){ b.pb(A[i]); } // reverse(all(b)); bad.clear(); for(int i = 0;i<n/2;i++){ int x = min(a[i],b[i]); if(n-x+1 != max(a[i],b[i])){ cout<<-1<<endl; return; } if(a[i] > b[i]){ bad.pb(i); isbad[i] = 1; } } if(bad.size()%2){ cout<<-1<<endl; return; } dox(); // print(a); // print(b); // dop(); for(auto i:ansx){ ans.pb({i[0]+1,n-i[1]}); } // print(a); // print(b); map<int,int>ind; for(int i = 0;i<n/2;i++){ ind[a[i]] = i; } for(int i = 1;i<=n/2;i++){ if(ind[i] != i-1){ int j = ind[i]; ans.pb({ind[i]+1,i}); swap(ind[i],ind[a[i-1]]); swap(a[i-1],a[j]); swap(b[j],b[i-1]); } } // for(int i = 0;i<n/2;i++){ // if(a[i] != i+1){ // int j = a[i]-1; // cout<<i+1<<" "<<j+1<<endl; // swap(a[i],a[j]); // swap(b[i],b[j]); // ans.pb({i+1,j+1}); // } // } cout<<ans.size()<<" "<<ans.size()<<endl; for(auto i:ans){ print(i); } // print(a); // print(b); ansx.clear(); ans.clear(); } signed main(){ ios::sync_with_stdio(0);//DO NOT USE IN INTERACTIVE cin.tie(0), cout.tie(0); cout << fixed<<setprecision(9); int t = 1; cin>>t; for(int i = 1;i<=t;i++){ solve(i); } }