API Change Request: add List.sortRange and List.shuffleRange

[jolleekin]

The List interface currently has several methods that operate on a range instead of the whole list such as fillRange, setRange, getRange, removeRange, and replaceRange. However, it doesn't have sortRange and shuffleRange. This makes it less efficient to use in some cases.

For example, in a coding competition like Google Code Jam, it's more efficient to instantiate a list once and reuse it for all test cases instead of instantiating it for every test case. This is only achievable if sortRange and shuffleRange are added.

/// Without `List.sortRange`, the list must be instantiated for every test case.

import 'dart:io';
import 'dart:typed_data';

void main() {
  final testCount = readInt();
  for (var testCase = 1; testCase <= testCount; ++testCase) {
    final n = readInt();
    final list = Int64List(n);
    for (var i = 0; i < n; ++i) {
      list[i] = readInt();
    }
    list.sort((x, y) => y - x);
  }
}

/// With `List.sortRange`, the list can be instantiated once and reused for all test cases.

import 'dart:io';
import 'dart:typed_data';

const maxN = 100000;
final list = Int64List(maxN);

void main() {
  final testCount = readInt();
  for (var testCase = 1; testCase <= testCount; ++testCase) {
    final n = readInt();
    for (var i = 0; i < n; ++i) {
      list[i] = readInt();
    }
    list.sortRange(0, n, (x, y) => y - x);
  }
}

Dart SDK version: 2.7.0

[lrhn]

We do not plan to change the List API at this time.
The best solution here would be extension methods supplied by package:collection.

Another option is to add a lazy sublist view, so you can do, say, ListSlice(source, start, end)..sort(). The list created by ListSlice would be a fixed-length list which represents a slice of the source list and operate entirely on that. I'm not aware of an available implementation of this, though.
(That's effectively how the Java List and String APIs work: You can get a lazy slice and do any operation you want on that, rather than every operation having to take a start and end).

[jolleekin]

The particular use case here is a coding competition, which makes your suggestions unfeasible

1. Using external packages is not allowed
2. List is much slower than typed lists such as Int64List. For some problems, using List results in time limit error while using typed lists (that are instantiated once) passes all test cases