Count Good Subsequences

Problem Overview

• Count good subsequences in an array, where a sequence is good if all elements are unique and all integers between its min and max appear.
• Input: int array arr of size n (1 ≤ n ≤ 1e5, 1 ≤ arr[i] ≤ 1e5); Output: long integer count of distinct subsequences by indices.
• Domain: array/subsequence processing, modeling contiguous value ranges in datasets.
• This coding interview problem is from Flexport interviews and is a common interview question.