Time a block of work — practice exercise

What you'll be asked to do

1. 1.Time a block of workexercise · easy · 10 min

   Measure how long a loop takes and confirm it is not negative.

   Passes when: #out should show true.

2. 2.Move work out of a loopexercise · easy · 10 min · practice plan

   Compute a value once outside the loop instead of every time.

   Passes when: #out should show PREFIX-a,PREFIX-b.

3. 3.Compare two equivalent approachesexercise · easy · 10 min · practice plan

   Show filter+map and a manual loop give the same result.

   Passes when: #out should show same result.

4. 4.Choose the faster membership checkexercise · easy · 10 min · practice plan

   Use a Set for a membership check instead of an array.

   Passes when: #out should show true.

5. 5.Keep code simple by defaultexercise · medium · 10 min · practice plan

   Show a simple reduce-based sum gives the correct total.

   Passes when: #out should show 10.

6. 6.Fix the work repeated every iterationbug fix · easy · 8 min

   The unchanging prefix should be computed once, not inside the loop.

   Passes when: #out should show 1.

7. 7.Fix includes used where has would scale betterbug fix · easy · 8 min · practice plan

   An array membership check is slower than a Set for repeated lookups.

   Passes when: #out should show true.

8. 8.Fix the elapsed time measured backwardsbug fix · easy · 8 min · practice plan

   The start time must be subtracted from the end time, not the other way round.

   Passes when: #out should show 500 ms elapsed.

9. 9.Fix the rewritten code that changed the answerbug fix · easy · 8 min · practice plan

   An optimisation attempt must still give the same result.

   Passes when: #out should show same result.

10. 10.Fix the total never reset between runsbug fix · easy · 8 min · practice plan

    Reusing the same total across two separate measurements corrupts the second.

    Passes when: #out should show 10.

Between them these tasks cover Measuring, Loop cost and Data structure choice.

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