Leetcode 3134. Find the Median of the Uniqueness Array

Find the median of the multiset formed by the number of distinct elements in every subarray of nums — i.e., determine the k-th smallest value of distinct(nums[i..j]) over all O(n^2) subarrays. Key insight: the predicate "number of subarrays with ≤ t distinct elements" is monotone and can be computed with a sliding-window frequency map, enabling a binary search over t to locate the median.