Find missing value in sorted consecutive array
Company: Arista
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
Given a sorted array `nums` of **distinct integers**. The numbers are supposed to form a consecutive sequence starting from some unknown integer `start`:
- If nothing is missing, the sequence would be: `start, start+1, start+2, ..., start+n-1` where `n = len(nums)`.
- But **at most one** number from this sequence may be missing in `nums`.
Return the missing number if one exists; otherwise return `null` (or `-1`, but be consistent).
**Requirements**
- Time complexity must be **O(log n)**.
- Space complexity must be **O(1)**.
**Examples**
- `nums = [4,5,6,8,9]` → missing is `7`
- `nums = [-3,-2,-1,0,1]` → no missing → return `null`
- `nums = [10,11,12,13,15]` → missing is `14`
**Notes**
- `start` can be any integer (including negative).
- `nums` is already sorted ascending and contains no duplicates.
Quick Answer: This question evaluates understanding of array properties and algorithmic complexity, specifically detecting a single missing element in a sorted consecutive sequence within the Coding & Algorithms category.
Given a sorted distinct array that should be consecutive except for at most one interior missing value, return the missing number or None if no value is missing.
Constraints
- nums is sorted ascending with distinct integers.
- At most one interior value is missing.
- Return None when no missing value is detectable.
Examples
Input: ([4,5,6,8,9],)
Expected Output: 7
Explanation: The first index whose value is offset too far reveals the missing number.
Input: ([-3,-2,-1,0,1],)
Expected Output: None
Explanation: A fully consecutive array returns None.
Hints
- For a perfect consecutive array, nums[i] - nums[0] equals i.
- Binary search for the first index where that invariant fails.