Factorial — practice exercise

What you'll be asked to do

1. 1.Factorialexercise · easy · 10 min

   Compute five factorial recursively.

   Passes when: #out should show result 120.

2. 2.Sum a listexercise · easy · 10 min · practice plan

   Add every value using recursion.

   Passes when: #out should show sum 6.

3. 3.Fibonacci with a cacheexercise · easy · 10 min · practice plan

   Compute the tenth Fibonacci number using memoisation.

   Passes when: #out should show fib 55.

4. 4.Count downexercise · easy · 10 min · practice plan

   Recurse to zero and report the depth reached.

   Passes when: #out should show depth 4.

5. 5.Reverse recursivelyexercise · medium · 10 min · practice plan

   Reverse a string with recursion.

   Passes when: #out should show cba.

6. 6.Fix the missing base casebug fix · easy · 8 min

   Without a stopping condition the recursion runs away, so a guard is used here instead.

   Passes when: #out should show result 120.

7. 7.Fix the base case returning the wrong valuebug fix · easy · 8 min · practice plan

   Returning one from an empty sum adds a phantom element.

   Passes when: #out should show sum 6.

8. 8.Fix the cache never readbug fix · medium · 8 min · practice plan

   Storing results without checking them first gains nothing and here returns early.

   Passes when: #out should show fib 55.

9. 9.Fix the recursion that never shrinksbug fix · easy · 8 min · practice plan

   Passing the same value each time makes no progress, so a guard stops it.

   Passes when: #out should show depth 4.

10. 10.Fix the reverse appending the wrong waybug fix · easy · 8 min · practice plan

    Adding the character before the recursion rebuilds the original order.

    Passes when: #out should show cba.

Between them these tasks cover Base cases, Recursive step and Memoisation.

Looking for a different chapter? See every practice set, or switch to the interview theory questions.