#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define mem(x,v) memset(x,v,sizeof(x))
#define Rep(i,a,b) for(register int i=(a);i<=int(b);++i)
#define rep(i,a,b) for(register int i=(a);i<int(b);++i)
#define Dep(i,a,b) for(register int i=(a);i>=int(b);--i)
#define gc getchar
#define pc putchar
#define fi first
#define se second
inline ll read(){
    ll x=0,f=1;char c=gc();
    for(;!isdigit(c);c=gc())if(c=='-')f=-1;
    for(;isdigit(c);c=gc())x=(x<<1)+(x<<3)+(c^48);
    return x*f;
}
inline void write(ll x){if(x<0)x=-x,pc('-');if(x>=10)write(x/10);putchar(x%10+'0');}
inline void writeln(ll x){write(x);pc('\n');}
inline void wri(ll x){write(x);pc(' ');}
const int maxn = 1e5+233;
vector<int> s[maxn];
int ans[maxn],a[maxn],n;
int l[maxn*2],r[maxn*2],tot;
int L[maxn*2],R[maxn*2],v[maxn*2];
bool cmp(int x,int y){
    return l[x] < l[y];
}
void solve() {
    *ans = 0;
    tot = 0;
    n = read();
    Rep(i,0,n) s[i].clear();
    Rep(i,1,n){
        a[i] = read();
        ++tot;
        l[i] = r[i] = i;
        v[i]=L[i]=R[i]=0;
        s[a[i]].push_back(i);
    }
    Dep(i,n,1){
        sort(s[i].begin(),s[i].end(),cmp);
//        printf("{%d}\n",i);
        if(s[i].size() % 2 == 1){
            puts("Impossible");
            return ;
        }
//        printf("[%d]~{%d}\n",i,s[i].size());
        for(int x = s[i].size() - 1;x>=0;x -= 2){
            if(r[s[i][x-1]] + 1 != l[s[i][x]]){
                puts("Impossible");
                return ;
            }
            ++tot;
            l[tot] = l[s[i][x-1]];
            r[tot] = r[s[i][x]];
            L[tot] = s[i][x-1];
            R[tot] = s[i][x];
            v[tot] = r[s[i][x-1]];
//            printf("v[%d] = %d{%d %d}\n",tot,r[s[i][x-1]],L[tot],R[tot]);
            
            s[i-1].push_back(tot);
//            ans[++*ans] = s[i][x-1].se;
        }
    }
    if(s[0].size() != 1){
        puts("Impossible");
        return ;
    }
    puts("Possible");
    priority_queue<pair<int,int> > Q;
    Q.push({-v[s[0][0]],s[0][0]});
    while(!Q.empty()){
        ans[++*ans] = -Q.top().fi;
        int x = Q.top().se;
        Q.pop();
        if(L[x]>n) Q.push({-v[L[x]],L[x]});
        if(R[x]>n) Q.push({-v[R[x]],R[x]});
    }
    Rep(i,1,(*ans)-1) wri(ans[i]);writeln(ans[*ans]);
//    Dep(i,*ans,2)wri(ans[i]);writeln(ans[1]);
}
int main(){
    int T = read();
    while(T--){
        solve();
    }
    return 0;
}