Count down — practice exercise

What you'll be asked to do

1. 1.Count downexercise · easy · 10 min

   Count down from 3 to 1 with recursion, collecting the numbers joined by a dash.

   Passes when: #out should show 3-2-1.

2. 2.Factorialexercise · easy · 10 min · practice plan

   Work out factorial of 5 with recursion.

   Passes when: #out should show 120.

3. 3.Add up an arrayexercise · easy · 10 min · practice plan

   Add every number in the array using recursion.

   Passes when: #out should show 10.

4. 4.Count nested itemsexercise · easy · 10 min · practice plan

   Count every item in a nested list, however deep it goes.

   Passes when: #out should show 6.

5. 5.Reverse a stringexercise · medium · 10 min · practice plan

   Reverse the word stream using recursion.

   Passes when: #out should show maerts.

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

   The base case returns the wrong starting value.

   Passes when: #out should show 120.

7. 7.Fix the value that never shrinksbug fix · easy · 8 min · practice plan

   The recursive call passes the same value, so nothing progresses.

   Passes when: #out should show 10.

8. 8.Fix the missing recursive callbug fix · easy · 8 min · practice plan

   Nested lists are counted as one item instead of being opened up.

   Passes when: #out should show 6.

9. 9.Fix the reversed join orderbug fix · easy · 8 min · practice plan

   The characters are put back together the wrong way round.

   Passes when: #out should show maerts.

10. 10.Fix the base case checked too latebug fix · easy · 8 min · practice plan

    The list is read before checking whether it is empty.

    Passes when: #out should show 0.

Between them these tasks cover Base case, Recursive case and Nested data.

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