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Find missing value in sorted consecutive array

AristaSoftware Engineer · Technical Screen
EasySoftware EngineerTechnical ScreenCoding & Algorithms

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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 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.