#include<bits/stdc++.h>

const int MAXN = 100005;

int n;
int a[MAXN], pre[MAXN], nxt[MAXN], ans[MAXN];

int read()
{
    int p = 0;
    char c = getchar();
    while (c < '0' || c > '9') c = getchar();
    while (c >= '0' && c <= '9')
        p = p * 10 + (c - '0'), c = getchar();
    return p;
}

int main()
{
    int T;
    T = read();
    while(T--)
    {
        n = read();
        for(int i = 1; i <= n; i++)
        {
            a[i] = read();
            pre[i] = i - 1, nxt[i] = i + 1;
        }
        a[0] = a[n + 1] = 0;
        pre[n + 1] = n, nxt[0] = 1;
        
        int now = n;
        bool tf = true;
        for(int i = n - 1; i >= 1; i--)
        {
            //printf("%d %d\n", now, pre[now]);
            while (now > 1 && a[now] != a[pre[now]]) now = pre[now];
            if (now == 1) 
            {
                tf = false;
                break;
            }
            
            ans[i] = pre[now];
            a[now]--;
            pre[now] = pre[pre[now]];
            nxt[pre[now]] = now;
            
            //for(int i = 1; i <= n; i++) printf("%d ", nxt[i]);
            //printf("\n");
            //for(int i = 1; i <= n; i++) printf("%d ", pre[i]);
            //printf("\n");            
            if (i > 1 && a[now] == 0) 
            {
                tf = false;
                break;
            }
            if (i == 1 && a[now] != 0) tf = false;
            now = nxt[now];
        }
        
        if (!tf) printf("Impossible\n"); 
        else 
        {
            printf("Possible\n");
            printf("%d", ans[1]);
            for(int i = 2; i <= n - 1; i++)
                printf(" %d", ans[i]);
            printf("\n");
        }    
    }
    return 0;
}