Add algorithm: single_number using XOR

maths/special_numbers/single_number.py

@@ -0,0 +1,15 @@
+def single_number(nums: list[int]) -> int:
+ """
+ Find the element that appears only once in a list
+ where every other element appears twice.
+
+ This algorithm uses bitwise XOR to cancel out duplicate numbers.
+ """
+ res = 0
+ for n in nums:
+ res ^= n
+ return res
+
+if __name__ == "__main__":
+ example = [4, 1, 2, 1, 2]
+ print(single_number(example)) # Output: 4