Here is my Python solution!

def maxMin(k, arr):
    arr.sort()
    unfairness = arr[k - 1] - arr[0]
    for i in range(1, len(arr) - k + 1):
        unfairness = min(arr[k + i - 1] - arr[i], unfairness)
    return unfairness

Java:

public static int maxMin(int k, List arr) {

    int[] arr2 = arr.stream().mapToInt(i -> i).toArray();

    //primitive arrays are faster

    Arrays.sort(arr2);

    int diff = Integer.MAX_VALUE;

    for (int j=0; j < arr2.length - k + 1; ++j) {

        if (arr2[j+k-1] - arr2[j] < diff) {

            diff = arr2[j+k-1] - arr2[j];

        }

    }
    return diff;
}

def maxMin(k, arr): return min(map(lambda x, y: abs(x - y), sorted(arr)[:-k + 1], sorted(arr)[k - 1:]))

JS

function maxMin(k, arr) {
  // sort - lowest to highest
  arr.sort((a, b) => a - b);

  // calculate unfairness of "first chunk" of size k
  let minUnfairness = arr[k - 1] - arr[0];

  for (let i = 1; i + k - 1 < arr.length; i++) {
    // calculate unfairness in "next chunk" of size k
    const unfairness = arr[i + k - 1] - arr[i];

    if (unfairness < minUnfairness) {
      minUnfairness = unfairness;
    }
  }

  return minUnfairness;
}

Java Solution

Collections.sort(arr);
int min=Integer.MAX_VALUE;
for(int i=0;i<arr.size()-k+1;i++){
    if((arr.get(i+k-1)-arr.get(i))<min)
    {
        min=arr.get(i+k-1)-arr.get(i);
    }
}
return min;

}