#include <bits/stdc++.h>
using namespace std;
const int maxn = 100100;
int x[maxn*4],f[maxn],mn[maxn],mx[maxn],a[maxn],ans[maxn];
int ch[maxn][2],c[maxn];
int fnd(int u) {
    return f[u]==u?u:(f[u]=fnd(f[u]));
}
void build(int l,int r,int rt) {
    if (l == r) {
        x[rt]=0;
        if (a[l] == a[l+1]) x[rt]=max(x[rt],l);
        return ;
    }
    int mid=(l+r)/2;
    build(l,mid,rt<<1);
    build(mid+1,r,rt<<1|1);
    x[rt] = max(x[rt<<1],x[rt<<1|1]);
}
void upd(int p,int l,int r,int rt) {
//    printf("upd %d [%d %d]\n",p,l,r);
    if (l == r) {
        int p1 = fnd(l), v1 = a[p1];
        int p2 = fnd(l+1), v2 = a[p2];
        if (p1!=p2 && v1==v2) x[rt]=l;
        else x[rt]=0;
        return ;
    }
    int mid=(l+r)/2;
    if (p <= mid) upd(p,l,mid,rt<<1);
    else upd(p,mid+1,r,rt<<1|1);
    x[rt] = max(x[rt<<1],x[rt<<1|1]);
}
int tot,n;
void dfs(int u) {
    tot++;
    printf("%d%c",u," \n"[tot==n-1]);
    if (ch[u][0]>ch[u][1]) swap(ch[u][0],ch[u][1]);
    for (int i=0;i<2;i++) if (ch[u][i]) {
        dfs(ch[u][i]);
    }
}
int main(void) {
//    freopen("e.in","r",stdin);
    int T; scanf("%d",&T);
    while (T--) {
        scanf("%d",&n);
        for (int i=1;i<=n;i++) scanf("%d",&a[i]);
        for (int i=1;i<=n;i++) f[i]=mn[i]=mx[i]=i,ch[i][0]=ch[i][1]=c[i]=0;
        build(1,n-1,1);
        int ok = 1;
        for (int i=n-1;i>=1;i--) {
//            printf("i = %d\n",i);
            if (x[1] == 0) {ok=0; break;}
            ans[i] = x[1];
            int fu = fnd(ans[i]), fv = fnd(ans[i]+1);
//            printf("x1 = %d\n",x[1]);
//            printf("fu = %d, fv = %d\n",fu,fv);
            int p = mn[fu], q = mx[fv];
            f[fu]=fv, a[fv]--, mn[fv]=mn[fu];
            ch[ans[i]][0] = c[fu];
            ch[ans[i]][1] = c[fv];
            c[fv] = ans[i];
//            printf("rt = %d, mn = %d, mx = %d\n",ans[i],p,q);
//            printf("upd %d %d %d\n",ans[i],p-1,q);
            upd(ans[i],1,n-1,1);
            if (p>1) upd(p-1,1,n-1,1);
            if (q<n) upd(q,1,n-1,1);
        }
//        printf("ok = %d\n",ok);
        if (ok == 0 || a[fnd(1)] != 0) printf("Impossible\n");
        else {
            printf("Possible\n");
            tot=0;
            dfs(ans[1]);
//            for (int i=1;i<n;i++) printf("%d%c",ans[i]," \n"[i==n-1]);
        }
    }
    return 0;
}