Find missing value in sorted consecutive array

Q: Find missing value in sorted consecutive array

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.

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Question

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.

Find missing value in sorted consecutive array

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