single_element_in_a_sorted_array.py

'''
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. 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.
'''

class Solution:
    def singleNonDuplicate(self, nums: list) -> int:
        #a = 2*sum(set(nums))-sum(nums)
        low=0
        high=len(nums)-1
        while low < high:
            mid=(low+high)//2
            if (mid%2==0 and nums[mid]==nums[mid+1]) or (mid%2==1 and nums[mid]==nums[mid-1]):
                low=mid+1
            else:
                high=mid
        return nums[low]

s=Solution()
a=s.singleNonDuplicate([1])
print(a)