#include<cstdio>
#include<cstring>
#include<cctype>
#include<queue>
#include<algorithm>
#include<vector>
#define pb push_back
#define mp make_pair
#define xx first
#define yy second
#define rep(i,a,b) for(int i=(a),i##_end_=(b);i<=i##_end_;i++)
#define dwn(i,a,b) for(int i=(a),i##_end_=(b);i>=i##_end_;i--)
using namespace std;
inline int read() {
    int x=0,f=1;char c=getchar();
    for(;!isdigit(c);c=getchar()) if(c=='-') f=-1;
    for(;isdigit(c);c=getchar()) x=x*10+c-'0';
    return x*f;
}
typedef long long ll;
typedef pair<int,int> pii;
const int maxn=200010;
pii sta[maxn];
int n,a[maxn],flag,lc[maxn],rc[maxn];
pii seg[maxn];
void dfs(int x) {
    if(x<=n) return;
    if(flag) flag=0;
    else putchar(' ');
    printf("%d",seg[lc[x]].yy);
    dfs(lc[x]);
    dfs(rc[x]);
}
int main() {
//    freopen("data.in","r",stdin);
//    freopen("data.ans","w",stdout);
    int T=read();
    while(T--) {
        n=read();
        rep(i,1,n) a[i]=read();
        int m=n,top=0;
        rep(i,1,n) {
            seg[i]=mp(i,i);
            sta[++top]=mp(a[i],i);
            while(top>1) {
                if(sta[top].xx==sta[top-1].xx) {
                    lc[++m]=sta[top-1].yy;
                    rc[m]=sta[top].yy;
                    seg[m]=mp(seg[sta[top-1].yy].xx,seg[sta[top].yy].yy);
                    top--;sta[top]=mp(sta[top].xx-1,m);
                }
                else break;
            }
        }
        if(top!=1||sta[top].xx) puts("Impossible"); 
        else {
            puts("Possible"); 
            flag=1;
            dfs(sta[top].yy);
            puts("");
        }
    }
    return 0;
}