#include <bits/stdc++.h>
using namespace std;
const int maxn = 3e5, inf = 1e9;
int t, n, a[maxn + 10], ndcnt;
int stk[maxn + 10], scnt, id[maxn + 10];
int lc[maxn * 2 + 10], rc[maxn * 2 + 10];
int ans[maxn * 2 + 10], acnt, sz[maxn * 2 + 10];

void dfs(int p) {
    sz[p] = 1;
    if (p <= n) return;
    else {
        dfs(lc[p]); dfs(rc[p]);
        sz[p] = sz[lc[p]] + sz[rc[p]];
    }
}

void dfs2(int p, int ls) {
    if (p <= n) {
        assert(p == ls); return;
    } else {
        ans[++acnt] = ls + sz[lc[p]] - 1;
        dfs2(lc[p], ls);
        dfs2(rc[p], ls + sz[lc[p]]);
    }
}

int main() {
    scanf("%d", &t);
    while (t--) {
        scanf("%d", &n);
        for (int i = 1; i <= n; ++i) scanf("%d", &a[i]);
        scnt = 0; ndcnt = n;
        for (int i = 1; i <= n; ++i) {
            stk[++scnt] = a[i]; id[scnt] = i;
            while (scnt >= 2 && stk[scnt] == stk[scnt - 1]) {
                ++ndcnt;
                lc[ndcnt] = id[scnt - 1];
                rc[ndcnt] = id[scnt];
                --scnt; --stk[scnt]; id[scnt] = ndcnt;
            }
        }
        if (scnt > 1 || stk[scnt] != 0) {
            printf("Impossible\n"); continue;
        }
        acnt = 0;
        dfs(id[1]);
        dfs2(id[1], 1);
        printf("Possible\n");
        assert(acnt == n - 1);
        for (int i = 1; i <= acnt; ++i)
            printf("%d%c", ans[i], " \n"[i == acnt]);
    }
}