#include <bits/stdc++.h>

using namespace std;

#define N 100007
#define p 1000000007
#define LL long long

struct node
{
    int x, id, next, pre;
} a[N];

vector<int> E[N * 2];

int ans[N * 2];

priority_queue<pair<int, int> > q;

int main()
{
    a[0].x = -N;
    int T, n, x, cnt;
    scanf("%d", &T);
    while (T--)
    {
        scanf("%d", &n);
        for(int i = 1; i <= n; i++)
        {
            scanf("%d", &x);
            a[i].x = x;
            a[i].id = i;
            a[i].next = i + 1;
            a[i].pre = i - 1;
        }
        cnt = n;
        for(int i = 1; i <= n + n; i++)
        {
            E[i].clear();
        }
        a[0].next = 1;
        a[n + 1].x = -N;
        a[n + 1].pre = n;
        int now = 1;
        while (now < n)
        {
            if (a[now].x != a[a[now].next].x)
            {
                now = a[now].next;
                continue;
            }
            cnt++;
            E[cnt].push_back(a[now].id);
            E[cnt].push_back(a[a[now].next].id);
            ans[cnt] = now;
            a[now].x--;
            now = a[now].pre;
            a[now].next = a[a[now].next].next;
            a[a[now].next].pre = now;
            a[a[now].next].x--;
            a[a[now].next].id = cnt;
        }
        if (a[n].x != 0 || a[n].pre != 0) printf("Impossible\n");
        else
        {
            printf("Possible\n");
            while (!q.empty()) q.pop();
            q.push(make_pair(-ans[cnt], cnt));
            bool check = false;
            while (!q.empty())
            {
                if (check) printf(" ");
                check = true;
                printf("%d", -q.top().first);
                x = q.top().second;
                q.pop();
                for (int j = 0; j < E[x].size(); j++)
                {
                    if (E[x][j] > n)
                    {
                        q.push(make_pair(-ans[E[x][j]], E[x][j]));
                    }
                }
            }
            printf("\n");
        }
    }
    return 0;
}