#include <stdio.h>
#include <algorithm>
#include <queue>

using namespace std;

struct node{
    int l,r,d;
} s[220000];
struct so{
    int i,l,d;
};
bool operator < (so x1,so x2){
    if(x1.d==x2.d)return x1.l>x2.l;
    return x1.d<x2.d;
}
int n;
int a[120000];
int ls[220000],rs[220000];
int tot;
int ans[120000],id;
priority_queue<so>q;
int f;
void clr(){
    int i;
    for(i=1;i<=tot;i++)ls[i]=rs[i]=0;
    for(i=1;i<=n;i++)ans[i]=0;
    tot=0;
    id=0;
    while(q.size())q.pop();
    f=0;
}
void addedge(int u,int v, int kind){
    //printf("ad%d %d %d\n",u,v,kind);
    if(kind==0)ls[u]=v;
    else rs[u]=v;
}
void dfs(int i, int d){
    //printf("%d %d\n",i,d);
    if(s[i].l==s[i].r){
        if(d!=s[i].d)f=0;
        return;
    }
    ans[++id]=s[ls[i]].r;
    dfs(ls[i],d+1);
    dfs(rs[i],d+1);
}
void xx(){
    int i;
    so t,y;
    scanf("%d",&n);
    clr();
    for(i=1;i<=n;i++){
        scanf("%d",&a[i]);
        s[i].l=s[i].r=i;
        s[i].d=a[i];
        t.i=i;t.l=i;t.d=a[i];
        q.push(t);
    }
    tot = n;
    while(q.size()>1){
        t=q.top();q.pop();
        if(q.top().d!=t.d) {
            printf("Impossible\n");
            return;
        }
        y=q.top();q.pop();
        if(s[t.i].r+1!=y.l) {
            printf("Impossible\n");
            return;
        }
        tot++;
        s[tot].l=t.l;s[tot].r=s[y.i].r;s[tot].d=t.d-1;
        addedge(tot,t.i,0);
        addedge(tot,y.i,1);
        t.i=tot;t.l=s[tot].l;t.d=s[tot].d;
        q.push(t);
    }
    f=1;
    dfs(tot,0);
    if(!f){
        printf("Impossible\n");
        return;
    }
    printf("Possible\n");
    for(i=1;i<=n-1;i++)printf("%d%c",ans[i],i==n-1?'\n':' ');
}
int main () {
    int t;
    scanf("%d",&t);
    while(t--)xx();
    return 0;
}