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540. Single Element in a Sorted Array

Difficulty Topics

Description

You are given a sorted array consisting of only integers where every element appears exactly twice, except for one element which appears exactly once.

Return the single element that appears only once.

Your solution must run in O(log n) time and O(1) space.

 

Example 1:

Input: nums = [1,1,2,3,3,4,4,8,8]
Output: 2

Example 2:

Input: nums = [3,3,7,7,10,11,11]
Output: 10

 

Constraints:

  • 1 <= nums.length <= 105
  • 0 <= nums[i] <= 105

Solution

single-element-in-a-sorted-array.py
class Solution:
    def singleNonDuplicate(self, nums: List[int]) -> int:

        left, right = 0, len(nums) - 1

        while left < right:
            mid = left + (right - left) // 2

            if (mid % 2 == 0 and nums[mid] == nums[mid + 1]) or (mid % 2 == 1 and nums[mid] == nums[mid - 1]):
                left = mid + 1
            else:
                right = mid

        return nums[left]