Count Number of Nice Subarrays

Given an array of integers nums and an integer k, return the number of nice subarrays. A nice subarray has exactly k odd numbers in it. Pattern: Prefix count / sliding window. Track count of odd numbers seen so far. For each position, if oddCount >= k, add count[oddCount - k] to result (number of previous positions where oddCount was exactly k less than now). This is the same technique as "number of subarrays with sum = k" (LC 560). Example 1: Input: nums = [1,1,2,1,1], k = 3 Output: 2 Explanation: [1,1,2,1] and [1,2,1,1] each have exactly 3 odd numbers. Example 2: Input: nums = [2,4,6], k = 1 Output: 0