add doctest/document to actual_power and document to power (#11187)

* Update power.py

* Update divide_and_conquer/power.py

---------

Co-authored-by: Tianyi Zheng <[email protected]>

Author: pedram-mohajer

divide_and_conquer/power.py

@@ -2,6 +2,20 @@ def actual_power(a: int, b: int):
     """
     Function using divide and conquer to calculate a^b.
     It only works for integer a,b.
+
+    :param a: The base of the power operation, an integer.
+    :param b: The exponent of the power operation, a non-negative integer.
+    :return: The result of a^b.
+
+    Examples:
+    >>> actual_power(3, 2)
+    9
+    >>> actual_power(5, 3)
+    125
+    >>> actual_power(2, 5)
+    32
+    >>> actual_power(7, 0)
+    1
     """
     if b == 0:
         return 1
@@ -13,6 +27,10 @@ def actual_power(a: int, b: int):
 
 def power(a: int, b: int) -> float:
     """
+    :param a: The base (integer).
+    :param b: The exponent (integer).
+    :return: The result of a^b, as a float for negative exponents.
+
     >>> power(4,6)
     4096
     >>> power(2,3)