How to reverse a list in dart

How to reverse a list in dart:

To revese a list in Dart, we have one inbuilt property called reversed. This property returns one iterable of the items in the list in reversed order. We can convert the iterable to a list using toList method.

Below is the definition of reversed :

Iterable<E> get reversed;

Example of reversing a list in Dart:

Let’s check how this property works :

void main() {
  var list = new List();
  list.add(1);
  list.add(2);
  list.add(3);
  
  print(list);
  var reversed = list.reversed;
  print(reversed.toList());
}

If you run this Dart program, it will print the below output:

[1, 2, 3]
[3, 2, 1]

As you can see here, the list is reversed.

Doing inplace reverse:

The above example created one new list. We can also do inplace reversing i.e. we can modify the original list without creating a new list. For that, we need one loop to iterate through the values and reverse them during iteration.

For example, consider the below list :

[1, 2, 3, 4, 5, 6, 7]

For inplace reverse,

We need to swap the element in position 0 with the element in position 6
Swap element in position 1 with element in position 5
i.e. swap element in position i with element in size - i - 1
We don’t need any swapping for element in position 3

So, for an even sized list or odd sized list, we can run one loop and swap all elements in ith position with the elements in size - i - 1th position.

Dart program:

void main() {
  var list = new List();
  list.add(1);
  list.add(2);
  list.add(3);
  list.add(4);
  list.add(5);
  list.add(6);
  list.add(7);

  print(list);

  for (var i = 0; i < list.length / 2; i++) {
    var tempValue = list[i];
    list[i] = list[list.length - 1 - i];
    list[list.length - 1 - i] = tempValue;
  }
  
  print(list);
}

Output:

The above program will print the below output:

[1, 2, 3, 4, 5, 6, 7]
[7, 6, 5, 4, 3, 2, 1]

It modifies the original list.

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How to reverse a list in dart