Count Distinct Elements in Subarray

[
  [
    1,
    2,
    1,
    3,
    4,
    2,
    3
  ],
  4
]

Explanation. The distinct counts for subarrays are: [1,2,1,3] -> 3 distinct elements, [2,1,3,4] -> 4 distinct elements, [1,3,4,2] -> 4 distinct elements, [3,4,2,3] -> 3 distinct elements.

[
  [
    1,
    1,
    1,
    1
  ],
  2
]

Explanation. Each subarray of size 2 has the same element repeated, so there is only 1 distinct element.

[
  [
    5,
    2,
    7,
    7,
    7,
    8,
    10
  ],
  3
]

Explanation. Distinct counts change as the window slides through the array. Distinct elements in subarrays are [5,2,7] -> 3, [2,7,7] -> 2, [7,7,7] -> 1, [7,7,8] -> 2, [7,8,10] -> 2.