#include <bits/stdc++.h>
#define ll long long
#define maxn 200005 /*rem*/
#define mod 998244353
#define db double
#define vi vector<int>
#define pb push_back
#define iter set<th>::iterator
using namespace std;
ll ksm(ll a, ll b) {
   if (!b) return 1;
   ll ns = ksm(a, b >> 1);
   ns = ns * ns % mod;
   if (b & 1) ns = ns * a % mod;
   return ns;
}
struct th {
    int l, r;
    bool operator < (const th &u)const {
        return l < u.l;
    }
}; 
int id[maxn], ch[maxn][2], pl[maxn];
vector<th> r[maxn];
int ot[maxn], ocnt;
void dfs(int a) {    
//    cout << "!@#!@#" << a << " " << pl[a] << " " << ch[a][0] << endl;
    if (ch[a][0]) ot[ocnt++] = pl[a], dfs(ch[a][0]), dfs(ch[a][1]);
}
int main() {
    int t;
    cin >> t;
    for (int i = 0; i < t; i++) {
        ocnt = 0;
        int n;
        scanf("%d", &n);
        int idcnt = n + 1;
        for (int j = 0; j < idcnt; j++)
            pl[j] = ch[j][0] = ch[j][1] = 0, 
            r[j].clear();
        for (int j = 1; j <= n; j++) {
            th u;
            u.l = u.r = j;
            int k;
            scanf("%d", &k);
            id[j] = j;
            r[k].pb(u);
        }
        int fl = 1;
        for (int i = n - 1; i >= 1; i--) {
            sort(r[i].begin(), r[i].end());
            if (r[i].size() & 1){
                fl = 0;
                break;
            }
            for (int j = 0; j < r[i].size(); j += 2) {
                th u = r[i][j], v = r[i][j + 1];
                if (v.l != u.r + 1) {
                    fl = 0;
                    break;
                }
                th fn;
                fn.l = u.l, fn.r = v.r;
                ch[idcnt][0] = id[u.r], ch[idcnt][1] = id[v.r];
                id[fn.r] = idcnt, pl[idcnt] = u.r;
                r[i - 1].pb(fn);
                idcnt++;
            }
        }
        if (r[0].size() != 1) fl = 0;
        if (!fl) {
            cout << "Impossible" << endl;
            continue;
        }
        cout << "Possible" << endl;
        dfs(idcnt - 1);
        for (int i = 0; i < ocnt; i++) {
            printf("%d", ot[i]);
            if (i == ocnt - 1) cout << endl;
            else printf(" ");
        }
    }
    return 0;
}