#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005;
int T, n, a[maxn], R[maxn];
vector<int> ans;
int main() {
    for (scanf("%d", &T); T--; ) {
        scanf("%d", &n);
        ans.clear();
        for (int i = 1; i <= n; ++i) {
            scanf("%d", a + i);
            R[i] = i + 1;
        }
        int cur = n - 1;
        while (cur > 0) {
            if (R[cur] > n) {
                --cur;
                continue;
            }
            int v1 = a[cur], v2 = a[R[cur]];
            if (v1 == v2 && v1 != 0) {
                ans.push_back(R[cur] - 1);
                R[cur] = R[R[cur]];
                --a[cur];
            } else --cur;
        }
        if ((int)ans.size() == n - 1 && a[1] == 0) {
            puts("Possible");
            for (int i = n - 2; i >= 0; --i) printf("%d%c", ans[i], " \n"[i == 0]);
        } else {
            puts("Impossible");
        }
    }
    return 0;
}