How to add and remove items from a Queue in Dart

How to add and remove items from a Queue in Dart:

The Queue class of Dart can be used to create a queue. There are different methods available to add and remove items from a queue. In this post, we will learn how to create a Queue and how to remove and add items from it with different examples.

How to create a queue with elements:

We can create an empty queue with the Queue() constructor. There is one more constructor available to create a queue with all elements from an iterable. It is:

Queue.from(Iterable it)

You can also use Queue.of:

Queue.of(Iterable<E> it)

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4]);
  print(q);
}

It keeps adding the elements of the iterable to the end of the queue. It will print:

{1, 2, 3, 4}

Add a single element with add():

The add() method takes one single element and adds it to the queue. It is defined as:

add(E e) -> void

Let’s try it with an example:

import 'dart:collection';

void main() {
  var q = Queue();
  q.add(1);
  q.add(2);
  print(q);
}

It will add 1 and 2 to the queue. It will print:

{1, 2}

Add all elements of an iterable, addAll:

The addAll method adds all elements of an iterable to the end of the queue. It is defined as:

addAll(Iterable<E> it) -> void

Example:

import 'dart:collection';

void main() {
  var q = Queue();
  q.addAll([1, 2, 3, 4]);
  q.addAll([5, 6]);
  
  print(q);
}

Output:

{1, 2, 3, 4, 5, 6}

Add elements to the beginning and end of a queue:

The Queue class provides two methods to add an element to the start and end of a queue. These are:

addFirst(E e) -> void
addLast(E e) -> void

For example,

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4]);
  q.addFirst(0);
  q.addLast(5);

  print(q);
}

It created the queue q with Queue.of and added 0 to the start and 5 to the end.

Output:

{0, 1, 2, 3, 4, 5}

Remove all elements from a queue:

The clear() method removes all elements of a queue:

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4]);
  q.clear();

  print(q);
}

It will print:

{}

Remove a single item from a queue:

We can pass an object to the remove method to remove a single instance from the queue.

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4]);
  q.remove(2);

  print(q);
}

It will print:

{1, 3, 4}

It removes a single instance of the value. If we have two instances, it will remove only one:

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4, 2]);
  q.remove(2);

  print(q);
}

It will remove only the first 2:

{1, 3, 4, 2}

Remove the first and the last element of a queue:

We can use the following methods to remove the first and the last elements of a queue:

removeFirst() -> E

removeLast() -> E

For example:

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4, 5]);
  q.removeFirst();
  q.removeLast();

  print(q);
}

It will remove 1 and 5.

{2, 3, 4}

Remove specific elements with removeWhere:

The removeWhere function takes one function as its parameter and removes all elements for those the function returns true. Its syntax is:

removeWhere(bool fn(E e)) -> void

Example:

import 'dart:collection';

void main() {
  var q = Queue.of([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
  q.removeWhere((e) => e % 2 == 0);

  print(q);
}

This program will remove all even items from the queue.

{1, 3, 5, 7, 9}

Refer:

Flutter Queue Doc

CodeVsColor

How to add and remove items from a Queue in Dart