#include<bits/stdc++.h>
using namespace std;
const int M=1e5+5;

int n;
int A[M];

int R[M],L[M];
void Link(int x,int y){R[x]=y,L[y]=x;}
void Del(int x){Link(L[x],R[x]);}
priority_queue<int>Q;
int Ans[M],ansc;
void Solve()
{
    for(int i=1;i<=n;i++)Link(i-1,i);Link(n,0);
    while(Q.size())Q.pop();
    for(int i=1;i<n;i++)if(A[i]==A[R[i]])Q.push(i);
    ansc=0;
    while(Q.size())
    {
        int u=Q.top();Q.pop();if(A[u]!=A[R[u]])continue;
        // printf("%d %d\n",u,A[u]);
        A[u]--;Ans[++ansc]=R[u]-1;
        if(A[u]==0)break;
        Del(R[u]);
        if(R[u] and A[u]==A[R[u]])Q.push(u);
        if(L[u] and A[u]==A[L[u]])Q.push(L[u]);
    }
    if(A[1] or ansc!=n-1){puts("Impossible");return;}
    puts("Possible");
    for(int i=ansc;i>=1;i--)printf("%d%c",Ans[i]," \n"[i==1]);
}

int main()
{
    int T;scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(int i=1;i<=n;i++)scanf("%d",&A[i]);
        Solve();
    }
    return 0;
}