Letter Queue Letter Queue
Elementary+
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In computer science, a queue is a particular kind of data type in which the entities in the collection are kept in order and the principal operations on the collection are the addition of entities to the rear terminal position (enqueue or push), and removal of entities from the front terminal position (dequeue or pop). This makes the queue a First-In-First-Out (FIFO) data structure. In a FIFO data structure, the first element added to the queue will be the first one to be removed. This is equivalent to the requirement that once a new element is added, all elements that were added before have to be removed before the new element can be removed.

We will emulate the queue process with Python. You are given a sequence of commands:
- "PUSH X" -- enqueue X , where X is a letter in uppercase.
- "POP" -- dequeue the front position. if the queue is empty, then do nothing.
The queue can only contain letters.

You should process all commands and assemble letters which remain in the queue in one word from the front to the rear of the queue.

Let's look at an example, here’s the sequence of commands:
["PUSH A", "POP", "POP", "PUSH Z", "PUSH D", "PUSH O", "POP", "PUSH T"]

Command Queue Note
PUSH A A Added "A" in the empty queue
POP Removed "A"
POP The queue is empty already
PUSH Z Z
PUSH D ZD
PUSH O ZDO
POP DO
PUSH T DOT The result

Input: A sequence of commands as a list of strings.

Output: The queue remaining as a string.

Example:

letter_queue(['PUSH A',
 'POP',
 'POP',
 'PUSH Z',
 'PUSH D',
 'PUSH O',
 'POP',
 'PUSH T']) == 'DOT'
letter_queue(['POP', 'POP']) == ''
letter_queue(['PUSH H', 'PUSH I']) == 'HI'
letter_queue([]) == ''

How it is used: Queues provide services in computer science, transportation, and operations research where various entities such as data, objects, persons, or events are stored and held to be processed later. In these contexts, the queue performs the function of a buffer.

Precondition:
0 ≤ len( commands ) ≤ 30;
all(re.match("\APUSH [A-Z]\Z", c) or re.match("\APOP\Z", c) for c in commands )

Settings
Code:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

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