Subarray Product Less Than K

When every array value is positive, maintain a window product and a left pointer. For each right, multiply in nums[right]. While product >= k, divide out nums[left] and advance left. Once the product is below k, every subarray ending at right and starting from left through right is valid, contributing right-left+1 to the count. The early return 0 for k <= 1 is essential because positive products are at least one. Positivity makes shrinking safe: removing a positive factor cannot increase the product, so validity is monotonic. Each element enters and leaves the window at most once, giving O(n) time and O(1) extra space. If zeros, negatives, or overflow are permitted, clarify the contract: the usual proof no longer directly applies and products may need a larger numeric type or another technique.