#include<bits/stdc++.h> 
#define For(i,j,k) for (int i=(int)(j);i<=(int)(k);i++)
#define Rep(i,j,k) for (int i=(int)(j);i>=(int)(k);i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define ll long long
#define fi first
#define se second
#define PB push_back
#define uint unsigned
#define ull unsigned ll 
using namespace std;
const int N=200005;
int a[N],ls[N],rs[N],q[N],at[N];
int n,nd,ans[N];
void getans(int x){
    if (x<=n) return;
    ans[++*ans]=at[ls[x]];
    getans(ls[x]);
    getans(rs[x]);
}
void solve(){
    scanf("%d",&n); nd=n; *q=0;
    For(i,1,2*n) ls[i]=rs[i]=0;
    For(i,1,n) scanf("%d",&a[i]);
    For(i,1,n){
        q[++*q]=i; at[i]=i;
        for (;(*q)>=2&&a[q[*q]]==a[q[(*q)-1]];){
            at[++nd]=at[q[*q]];
            ls[nd]=q[(*q)-1];
            rs[nd]=q[*q];
            a[nd]=a[q[*q]]-1;
            --*q; --*q;
            q[++*q]=nd;
        }
    }
    if ((*q)!=1||a[q[1]]){
        puts("Impossible");
        return;
    }
    *ans=0;
    getans(q[1]);
    puts("Possible");
    For(i,1,n-1) printf("%d%c",ans[i],i==n-1?'\n':' ');
}
int main(){
    int T;
    scanf("%d",&T);
    while (T--) solve();
}