Stacks and Queues · Coding problem

Implement Queue using Arrays

A free coding problem from the Array-Backed Stack and Queue skill. Read it here, then solve it in the app in Java or Python.

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  • Java and Python

The problem

Implement a fixed-capacity queue backed by a plain array (a circular buffer; in Python, a list preallocated with [0] * capacity), supporting:

  • enqueue(x) - add a value to the back.
  • dequeue() - remove and return the front value, or -1 if empty.

Input format

Line 1: capacity. Line 2: q, the number of operations. Each of the next q lines is ENQUEUE x or DEQUEUE. For each DEQUEUE, print the result.

Example

Input:
3
5
ENQUEUE 1
ENQUEUE 2
ENQUEUE 3
DEQUEUE
ENQUEUE 4

Output:
1

After dequeuing 1, there's room to enqueue 4 even though the array only has capacity 3 - the freed slot at the front is reused.

Constraints

  • 1 <= capacity <= 10^4
  • 1 <= q <= 10^4
  • 0 <= x <= 10^9, so the empty result -1 never collides with a stored value
  • The queue never holds more than capacity elements at once

How it's graded

  • Run checks your code against the examples. Submit also runs a hidden suite in four groups - basic cases, edge cases, random inputs and performance tests at the size limit - and shows which groups pass, never the hidden inputs.
  • Stuck? Hints come in four steps, from a nudge to a code skeleton, each costing part of the points.
  • Once you pass, you see the approaches from brute force to optimal, and where your solution lands among them.

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