#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
const int M=200010;
struct point{
    int dep,left,right,node;
}h[M];
int cas,n,Cnt,x,lson[M],rson[M],split[M],ans[M];
void dfs(int u){
    if (u<=n)return;
    ans[++Cnt]=split[u];
    dfs(lson[u]);
    dfs(rson[u]);
}
int main(){
    scanf("%d",&cas);
    while (cas--){
        Cnt=0;
        scanf("%d",&n);
        for (int i=1;i<=n*2;i++)lson[i]=rson[i]=split[i]=0;
        int cnt=n,top=0;
        for (int i=1;i<=n;i++){
            scanf("%d",&x);
            h[++top].dep=x;
            h[top].left=i;
            h[top].right=i;
            h[top].node=i;
            while (top>1&&h[top].dep==h[top-1].dep){
                top--;
                h[top].dep--;
                cnt++;
                lson[cnt]=h[top].node;
                rson[cnt]=h[top+1].node;
                split[cnt]=h[top].right;
                h[top].node=cnt;
                h[top].right=h[top+1].right;
            }
        }
        if (top!=1||h[top].dep!=0){
            puts("Impossible");
            continue;
        }
        puts("Possible");
        dfs(h[top].node);
        for (int i=1;i<n-1;i++)printf("%d ",ans[i]);printf("%d\n",ans[n-1]);
    }
}