## Description

You've been working with a lot of different file types recently as your interests have broadened.

But what file types are you using the most? With this question in mind we look at the following problem.

Given a `List/Array` of Filenames (strings) `files` return a `List/Array of string(s)` contatining the most common extension(s). If there is a tie, return a sorted list of all extensions.

### Important Info:

* Don't forget, you've been working with a lot of different file types, so expect some interesting extensions/file names/lengths in the random tests.
* Filenames and extensions will only contain letters (case sensitive), and numbers.
* If a file has multiple extensions (ie: `mysong.mp3.als`) only count the the last extension (`.als` in this case)


## Examples

```
files = ['Lakey - Better days.mp3', 
         'Wheathan - Superlove.wav', 
         'groovy jam.als', 
         '#4 final mixdown.als', 
         'album cover.ps', 
         'good nights.mp3']
```

would return: `['.als', '.mp3']`, as both of the extensions appear two times in files.

```
files = ['Lakey - Better days.mp3', 
         'Fisher - Stop it.mp3', 
         'Fisher - Losing it.mp3', 
         '#4 final mixdown.als', 
         'album cover.ps', 
         'good nights.mp3']
```
would return `['.mp3']`, because it appears more times then any other extension, and no other extension has an equal amount of appearences.

```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\nimport re\n\ndef solve(files):\n    c = Counter(re.match('.*(\\.[^.]+)$', fn).group(1) for fn in files)\n    m = max(c.values(),default=0)\n    return sorted(k for k in c if c[k] == m)"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'solve'
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: 39622