"""
Some recursive functions
"""

# David Kauchak
# 11/14/2011

def factorial_iterative(n):
    """ Returns the factorial of n, iteratively """
    num = 1
    
    for i in range(2, n+1):
        num *= i
    
    return num

def factorial(n):
    """ Returns the factorial of n, recursively """
    # check the base case
    if n == 0:
        return 1
    else:
        # the recursive case
        return n * factorial(n-1)   
    
def factorial_interesting(n):
    """ a one-line way of calculating factorial.
    it's not recursive, but kind of cool :)
    """
    return eval(str(range(2,n+1))\
                .replace('[',"")\
                .replace(']',"")\
                .replace(", ", "*"))
    
def reverse(some_string):
    """ Returns the reverse of the input string """
    if len(some_string) == 0:
        return ""
    else:
        temp = some_string[-1] + reverse(some_string[:-1])
        print "Returning: " + temp        
        return temp

def power(base, exponent):
    """ Returns the base^exponent """
    if exponent == 0:
        return 1
    else:
        return base * power(base, exponent-1)
    
def fast_power(base, exponent):
    """ Returns the base^exponent """
    if exponent == 0:
        return 1
    elif exponent % 2 == 0:
        # b^e = b^(e/2) * b^(e/2)
        temp = fast_power(base, exponent/2)
        return temp * temp
    else:
        return base * fast_power(base, exponent-1)