Add algorithm: single_number using XOR

Author: komalharshita

maths/special_numbers/a_very_big_sum.py

@@ -0,0 +1,22 @@
+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.
+
+    >>> single_number([2, 2, 1])
+    1
+    >>> single_number([4, 1, 2, 1, 2])
+    4
+    >>> single_number([1])
+    1
+    """
+    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