We define the "unfairness" of a list/array as the *minimal* difference between max(x1,x2,...xk) and min(x1,x2,...xk), for all possible combinations of k elements you can take from the list/array; both minimum and maximum of an empty list/array are considered to be 0.

**More info and constraints:**

* lists/arrays can contain values repeated more than once, plus there are usually more combinations that generate the required minimum;
* the list/array's length can be any value from 0 to 10^(6);
* the value of k will range from 0 to the length of the list/array,
* the minimum unfairness of an array/list with less than 2 elements is 0.

For example:

```python
min_unfairness([30,100,1000,150,60,250,10,120,20],3)==20 #from max(30,10,20)-min(30,10,20)==20, minimum unfairness in this sample
min_unfairness([30,100,1000,150,60,250,10,120,20],5)==90 #from max(30,100,60,10,20)-min(30,100,60,10,20)==90, minimum unfairness in this sample
min_unfairness([1,1,1,1,1,1,1,1,1,2,2,2,2,2,2],10)==1 #from max(1,1,1,1,1,1,1,1,1,2)-min(1,1,1,1,1,1,1,1,1,2)==1, minimum unfairness in this sample
min_unfairness([1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1],10)==0 #from max(1,1,1,1,1,1,1,1,1,1)-min(1,1,1,1,1,1,1,1,1,1)==0, minimum unfairness in this sample
min_unfairness([1,1,-1],2)==0 #from max(1,1)-min(1,1)==0, minimum unfairness in this sample
```

**Note:** shamelessly taken from [here](https://www.hackerrank.com/challenges/angry-children), where it was created and debatably categorized and ranked.

```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 = 'def min_unfairness(arr,k):\n    arr = sorted(arr)\n    return min(b - a for a, b in zip(arr, arr[k-1:])) if arr and k else 0'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'min_unfairness'
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: 6010