solution.py

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