diff --git a/python/0540-single-element-in-a-sorted-array.py b/python/0540-single-element-in-a-sorted-array.py
new file mode 100644
index 000000000..10bf1ac9c
--- /dev/null
+++ b/python/0540-single-element-in-a-sorted-array.py
@@ -0,0 +1,27 @@
+class Solution:
+    def singleNonDuplicate(self, nums: List[int]) -> int:
+        def is_non_duplicate(i):
+            is_left_different = i == 0 or nums[i-1] != nums[i]
+            is_right_different = i == len(nums)-1 or nums[i+1] != nums[i]
+            return is_left_different and is_right_different
+
+        if len(nums) == 1:
+            return nums[0]
+
+        l, r = 0, len(nums) - 1
+        while l <= r:
+            mid = (l + r) // 2
+            if is_non_duplicate(mid):
+                return nums[mid]
+
+            if mid % 2 == 0:
+                if nums[mid+1] == nums[mid]:
+                    l = mid + 1
+                else:
+                    r = mid - 1
+            else:
+                if nums[mid+1] == nums[mid]:
+                    r = mid - 1
+                else:
+                    l = mid + 1
+