Example 1:
Input: heights = [1,5,3,9,7], gap = 2
Output: 2
Explanation:
Example 2:
Input: heights = [10,20,30,40], gap = 3
Output: 30
Explanation:
Example 3:
Input: heights = [1,2,3], gap = 5
Output: -1
Explanation:
You are given an integer array heights representing the heights of mountain peaks along a ridge (in index order) and an integer gap.
Return the minimum value of |heights[i] - heights[j]| over all index pairs (i, j) with |i - j| >= gap.
If no such pair exists (i.e., gap exceeds the largest possible index distance heights.length - 1), return -1.
This was reported from a Roblox online assessment (August 2025) as the second of two coding tasks in a 50-minute round.
Valid pairs (|i - j| >= 2): (0,2)|1-3|=2, (0,3)|1-9|=8, (0,4)|1-7|=6, (1,3)|5-9|=4, (1,4)|5-7|=2, (2,4)|3-7|=4. Minimum is 2.
Only (0,3) satisfies |i - j| >= 3, giving |10 - 40| = 30.
No index pair is 5 apart in a length-3 array, so return -1.
1 <= heights.length <= 10^40 <= heights[i] <= 10^91 <= gap <= 10^4