Find missing ranges in interval

Given a sorted unique integer array nums and two integers lower and upper defining an inclusive interval [lower, upper], return all missing ranges not present in nums within this interval. Format each missing range as "a" for single numbers or "a->b" for ranges. Consider cases where nums is empty, elements fall outside [lower, upper], or boundaries approach 32-bit integer limits. Aim for O(n) time and O(1) extra space (excluding output).

Find Missing Ranges in Interval

Given a sorted unique integer array nums and two integers lower and upper defining an inclusive interval [lower, upper], return a list of all the missing ranges — the maximal subranges of [lower, upper] whose every integer is absent from nums.

Format each missing range as a string:

• "a" if the range is a single number a.
• "a->b" if the range spans more than one number, from a to b inclusive.

Return the ranges in ascending order. Every element of nums lies within [lower, upper], nums is sorted in strictly increasing order (no duplicates), and the values may approach 32-bit signed integer limits, so be careful not to overflow when checking adjacency.

Return an empty list if every integer in [lower, upper] is present in nums.

Constraints

• -2^31 <= lower <= upper <= 2^31 - 1
• 0 <= nums.length <= 100
• lower <= nums[i] <= upper for every i
• nums is sorted in strictly increasing order (all elements unique)

Examples

Example 1

Input: ([0, 1, 3, 50, 75], 0, 99)
Output: ['2', '4->49', '51->74', '76->99']

Explanation: Within [0,99]: 2 is missing (single), 4..49 missing, 51..74 missing, and 76..99 missing up to the upper bound.

Example 2

Input: ([], 1, 1)
Output: ['1']

Explanation: nums is empty and the interval [1,1] is a single integer, so the whole interval is one missing single-number range.

Hints

1. Walk through the gaps between consecutive 'covered' points. Seed a prev value at lower - 1 so the first real gap is measured from the left boundary, and treat upper + 1 as a virtual element after the last real one so the final gap up to upper is captured.
2. A missing range exists between two adjacent covered values prev and cur exactly when there is at least one integer strictly between them — i.e. when cur - prev >= 2. The missing range is then [prev + 1, cur - 1].
3. To avoid 32-bit overflow at INT_MIN / INT_MAX, compare the gap with subtraction (cur - prev >= 2) rather than computing prev + 1 or cur + 1 before you know a gap exists, and only form the boundary values once you've confirmed the gap.