`Description:`

Given an input array (`arr`) of positive integers, the objective is to return an output array where each index represents the amount of times an element appeared (frequency) in the input array. 

More specifically, the element at each index of the output array will be an array (bucket) containing integers that appeared index-amount-of-times. 

Otherwise, slot nulls (JavaScript, Java), None's (Python) nils (Ruby), or NULL's (C/C++) where appropriate. A valid array will always be provided.

If an array of [1,2,3,4,4,5,5,5] is passed in, the expected output should be: [null, [1,2,3], [4], [5], null, null, null, null, null].

`Explanation:`

```python
# bucketize(arr) ======> outputArray
bucketize(1,2,3,4,4,5,5,5) ======> [None, [1, 2, 3], [4], [5], None, None, None, None, None]
```

An element cannot appear 0 times, so a null is placed at outputArray[0]. The elements 1, 2, and 3 appear once. This is why they are located at outputArray[1]. Notice the elements are grouped together in an array and sorted in ascending order. The element 4 appears twice. This is why it is located at outputArray[2]. The element 5 appears three times. This is why it is located at outputArray[3]. 

Although an integer could have possibly appeared four, five, six, seven, or eight times, this is not the case for this particular example. This is the reason why the elements at outputArray[4], outputArray[5], outputArray[6], outputArray[7], and outputArray[8] are all null values.

`Examples:`

```python
bucketize(2,2,4,4,6,6,9,9,9,9) ==> [None, None, [2,4,6], None, [9], None, None, None, None, None, None]
bucketize(3,3,3,3,2) ============> [None, [2], None, None, [3], None]
bucketize(5,5,5,5,5) ============> [None, None, None, None, None, [5]]
bucketize(77,3,40,40,40) ========> [None, [3,77], None, [40], None, None]
bucketize(16,7,5,3,6,23) ========> [None, [3,5,6,7,16,23], None, None, None, None, None]
```

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = 'from collections import Counter\nfrom bisect import insort\n\ndef bucketize(*arr):\n    c = Counter(arr)\n    xs = [None] * (len(arr) + 1)\n    for key, cnt in c.items():\n        if xs[cnt] is None:\n            xs[cnt] = []\n        insort(xs[cnt], key)\n    return xs'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'bucketize'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 9832