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Geeks of Coding

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Posts
• #946
Abhishek Tyagi
Keymaster

1. What is recursion used for?

Recursion lets us tackle complex problems by reducing the problem to a simpler one.

2. Which of these activities are good use cases for recursive programs? Check all that apply.

Going through a file system collecting information related to directories and files.
Managing permissions assigned to groups inside a company, when each group can contain both subgroups and users.

3. Fill in the blanks to make the is_power_of function return whether the number is a power of the given base. Note: base is assumed to be a positive number. Tip: for functions that return a boolean value, you can return the result of a comparison.

``````def is_power_of(number, base):
# Base case: when number is smaller than base.
if (number < base) and (number==1):
# If number is equal to 1, it's a power (base**0).
return True
elif (number == 0):
return False
else:
number = number / base
# Recursive case: keep dividing number by base.
return is_power_of(number, base)

print(is_power_of(8,2)) # Should be True
print(is_power_of(64,4)) # Should be True
print(is_power_of(70,10)) # Should be False``````

4. The count_users function recursively counts the amount of users that belong to a group in the company system, by going through each of the members of a group and if one of them is a group, recursively calling the function and counting the members. But it has a bug! Can you spot the problem and fix it?

``````def count_users(group):
count = 0
for member in get_members(group):
if is_group(member):
count += count_users(member)
else:
count += 1
return count

print(count_users("sales")) # Should be 3
print(count_users("engineering")) # Should be 8
print(count_users("everyone")) # Should be 18``````

5. Implement the sum_positive_numbers function, as a recursive function that returns the sum of all positive numbers between the number n received and 1. For example, when n is 3 it should return 1+2+3=6, and when n is 5 it should return 1+2+3+4+5=15

``````def sum_positive_numbers(n):