Find shortest subarray with range ≥ k

Problem

You are given an integer array nums of length n and an integer k.

Define the range of a subarray as:

[ \max(\text{subarray}) - \min(\text{subarray}) ]

Return the length of the shortest non-empty contiguous subarray whose range is at least k.

If no such subarray exists, return -1.

Input

• nums: array of integers (can include negatives)
• k: non-negative integer

Output

• An integer: the minimum length of a qualifying subarray, or -1 if none exists.

Constraints (typical interview scale)

• 1 <= n <= 2 * 10^5
• -10^9 <= nums[i] <= 10^9
• 0 <= k <= 10^9

Examples

• nums = [1, 3, 2], k = 2 → answer 2 (subarray [1,3] has range 2)
• nums = [5, 5, 5], k = 1 → answer -1