Single Element in a Sorted Array — LeetCode 540 Python Solution

The problem

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.

Example

Input

nums = [1,1,2,3,3,4,4,8,8]

Output

2

Python solution

class Solution:
    def singleNonDuplicate(self, nums: List[int]) -> int:
        l, r = 0, len(nums) - 1
        while l < r:
            mid = (l + r) >> 1
            if nums[mid] != nums[mid ^ 1]:
                r = mid
            else:
                l = mid + 1
        return nums[l]

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 540. Single Element in a Sorted Array is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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