Add sum (#24)

* sum to n recursion

* add sum_big_numbers

* Formatted with psf/black

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: realDuYuanChao

maths/sum_big_numbers.py

@@ -0,0 +1,12 @@
+def sum_big_numbers(first_number: int, second_number: int):
+    """
+    >>> sum_big_numbers(1234567891011121314151617181920, 2019181716151413121110987654321)
+    3253749607162534435262604836241
+    """
+    return first_number + second_number
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()

maths/sum_to_n_recursion.py

@@ -0,0 +1,16 @@
+def sum_to_n_recursion(number: int) -> int:
+    """
+    >>> sum_to_n_recursion(0)
+    0
+    >>> sum_to_n_recursion(10)
+    55
+    >>> sum_to_n_recursion(100)
+    5050
+    """
+    return 0 if number == 0 else number + sum_to_n_recursion(number - 1)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()