#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define REP(i,n) for(int i=(0);i<(n);i++)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
using namespace std;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef long long ll;

template<class T> inline void read(T &x){
    int f=0;x=0;char ch=getchar();
    for(;!isdigit(ch);ch=getchar())f|=(ch=='-');
    for(;isdigit(ch);ch=getchar())x=x*10+ch-'0';
    if(f)x=-x;
}

const int N=100005;
int s[N][3],a[N],n,top,rt;
priority_queue<int,vector<int>,greater<int> > Q;
vi e[N];

void MAIN(){
    read(n);
    rep(i,1,n)e[i].clear();
    top=0;
    rep(i,1,n){
        read(a[i]);
        s[++top][0]=a[i];
        s[top][1]=0;
        s[top][2]=i;
        while(top>=2&&s[top-1][0]==s[top][0]){
            top--;
            e[s[top][2]].pb(s[top][1]);
            e[s[top][2]].pb(s[top+1][1]);
            s[top][0]--;
            s[top][1]=s[top][2];
            s[top][2]=s[top+1][2];
        }
    }
    //printf("%d %d\n",top,s[top][0]);
    if(top>1||s[top][0]!=0){
        puts("Impossible");
        return;
    }
    puts("Possible");
    rt=s[top][1];
    Q.push(rt);
    int fir=1;
    while(!Q.empty()){
        int x=Q.top();
        Q.pop();
        if(!fir)putchar(' ');
        else fir=0;
        printf("%d",x);
        for(auto y:e[x])
            if(y)Q.push(y);
    }
    puts("");
}

int main(){
    int T;
    read(T);
    while(T--)
        MAIN();
    
    return 0;
}