Practice Recursion in CS Thinking
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
A technique where a function calls itself to solve progressively smaller instances of the same problem.
Russian dolls—open one, find a smaller one inside. Repeat until you reach the smallest.
Example 1
hardTrace the recursive function: FUNCTION factorial(n): IF n <= 1 THEN RETURN 1. ELSE RETURN n * factorial(n-1). Call factorial(4).
Example 2
hardWhat happens if a recursive function has no base case? For example: FUNCTION forever(n): RETURN forever(n+1).
Example 3
hardWrite a recursive function `sum(n)` that returns the sum 1 + 2 + ... + n. Trace sum(5).
Example 4
hardTrace `countdown(3)` for `FUNCTION countdown(n): OUTPUT n. IF n > 0 THEN countdown(n-1)`. What is printed, and what is the base case?