#include<bits/stdc++.h>

using namespace std;
#define ll long long

const int N = 100005;
int T, n, fuckbestcoder, stk[N], f[N], id[N], lson[N<<1], rson[N<<1], ans[N<<1];
void dfs(int u){
    if(ans[u]){
        printf("%d%c", ans[u], " \n"[++fuckbestcoder==n-1]);
        dfs(lson[u]), dfs(rson[u]);
    }
}
int main() {
    scanf("%d", &T);
    while(T--){
        scanf("%d", &n);
        int cnt=0, top=0;
        for(int i=1; i<=n; ++i){
            scanf("%d", ++top+stk);
            f[top]=i, id[top]=++cnt;
            while(top>1 && stk[top]==stk[top-1]){
                ++cnt;
                lson[cnt]=id[top-1], rson[cnt]=id[top], ans[cnt]=f[top-1];
                --stk[--top], f[top]=i, id[top]=cnt;
            }
        }
        if(top==1 && !stk[top]){
            puts("Possible");
            fuckbestcoder=0;
            dfs(cnt);
        }
        else puts("Impossible");
        memset(ans+1, 0, cnt<<2);
    }
    return 0;
}