540. Single Element in a Sorted Array

Description

Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element that appears only once.

Example 1:
Input: [1,1,2,3,3,4,4,8,8]
Output: 2

Example 2:
Input: [3,3,7,7,10,11,11]
Output: 10

Note: Your solution should run in $O(\log n)$ time and $O(1)$ space.

Solution

class Solution(object):
    def singleNonDuplicate(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        left, right = 0, len(nums)-1
        while left<right:
            mid = (left+right)//2
            if mid%2:
                if nums[mid]==nums[mid+1]:
                    right = mid - 1
                elif mid-1>=0 and nums[mid]==nums[mid-1]:
                    left = mid + 1
                else:
                    return nums[mid]
            else:
                if nums[mid]==nums[mid+1]:
                    left = mid + 2
                elif mid-1>=0 and nums[mid]==nums[mid-1]:
                    right = mid + 1
                else:
                    return nums[mid]
        return nums[left]