Count subarrays with at least k fruit pairs

Given an integer array nums where each value denotes a fruit type, and an integer k: For any subarray, define a 'pair' for fruit value v if its frequency in the subarray is at least 2; each fruit contributes at most one pair regardless of appearing more than twice. Return the number of subarrays whose number of such pairs is at least k. Example: nums = [0, 1, 0, 1, 0], k = 2 → 3 (valid subarrays are [0, 1, 0, 1], [1, 0, 1, 0], and [0, 1, 0, 1, 0]). Design an algorithm better than O(n^ 2), explain your approach (e.g., sliding window or two pointers), and analyze complexity.