added Python solution to 540. Single Element in a Sorted Array

Python/540.single_element_in_a_sorted_array.py

@@ -0,0 +1,29 @@
+"""
+540. Single Element in a Sorted Array
+
+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.
+
+Time Complexity: O(log n)
+"""
+
+
+
+def singleNonDuplicate(self, nums: List[int]) -> int:
+ l, r = 0, len(nums)-1
+
+ while l <= r:
+ mid = (l+r)//2
+
+ if mid==0 or mid==len(nums)-1 or \
+ (nums[mid] != nums[mid-1] and nums[mid] != nums[mid+1]):
+ return nums[mid]
+
+ if (mid % 2 == 0 and nums[mid] == nums[mid+1]) or \
+ (mid % 2 == 1 and nums[mid] == nums[mid-1]):
+ l = mid+1
+ else:
+ r = mid-1