Enqueue and dequeue — practice exercise

What you'll be asked to do

1. 1.Enqueue and dequeueexercise · easy · 10 min

   Add three values, remove the first, and join what remains.

   Passes when: #out should show 2-3.

2. 2.Peek the frontexercise · easy · 10 min · practice plan

   Show the value at the front without removing it.

   Passes when: #out should show front 1.

3. 3.Dequeue with a pointerexercise · easy · 10 min · practice plan

   Use an index instead of shift and show the value removed.

   Passes when: #out should show took 1.

4. 4.Queue size with a pointerexercise · easy · 10 min · practice plan

   Report how many items remain after two pointer dequeues.

   Passes when: #out should show one left.

5. 5.Level order walkexercise · medium · 10 min · practice plan

   Walk a small tree breadth first and join the values seen.

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

6. 6.Fix pop used as dequeuebug fix · easy · 8 min

   pop removes from the back, so the queue behaves like a stack.

   Passes when: #out should show 2-3.

7. 7.Fix the peek reading the backbug fix · easy · 8 min · practice plan

   The front of a queue is index zero, not the last slot.

   Passes when: #out should show front 1.

8. 8.Fix the pointer never advancingbug fix · easy · 8 min · practice plan

   Without moving head, the same item is dequeued forever.

   Passes when: #out should show took 2.

9. 9.Fix the size counted from lengthbug fix · easy · 8 min · practice plan

   With a pointer queue, length still counts the items already removed.

   Passes when: #out should show one left.

10. 10.Fix the breadth-first walk using a stackbug fix · medium · 8 min · practice plan

    Taking from the back turns the level order into a depth-first walk.

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

Between them these tasks cover Enqueue and dequeue, Pointer queues and BFS order.

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