Problem Description

Given a sorted array nums of distinct integers. These numbers are expected to form a consecutive sequence starting from an unknown integer start.

• If no number is missing, the sequence would be start, start+1, start+2, ..., start+n-1, where n is the length of nums.
• At most one number from this expected sequence may be missing in nums.

Your task is to return the missing number if one exists. If no number is missing, return null (or -1, ensuring consistency in your chosen return value).

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

• The start integer can be any value, including negative numbers.
• The input array nums is guaranteed to be sorted in ascending order and contains no duplicate values.