How do I reverse a String in Dart?

Question

I have a String, and I would like to reverse it. For example, I am writing an AngularDart filter that reverses a string. It\'s just for demonstration purposes, but it made me wo

Answer 1

There are many ways to reverse a string in Dart, some of them are given below.

Use split and join:

String reverseStringUsingSplit(String input) {
  var chars = input.split('');
  return chars.reversed.join();
}



Use runes:

String reverseStringUsingRunes(String input) {
  var chars = input.runes.toList();

  return String.fromCharCodes(chars.reversed);
}



Use codeUnits:

String reverseStringUsingCodeUnits(String input) {
  return String.fromCharCodes(input.codeUnits.reversed);
}

You can simply use all methods like this

void main() {
  var coflutter = 'Coflutter';

  print(reverseStringUsingSplit(coflutter));
  print(reverseStringUsingRunes(coflutter));
  print(reverseStringUsingCodeUnits(coflutter));
}

The output of all 3 methods will be

rettulfoC
rettulfoC
rettulfoC

Ref: https://coflutter.com/dart-how-to-reverse-a-string/

Answer 2

Try this function

String reverse(String s) {
  var chars = s.splitChars();
  var len   = s.length - 1;
  var i     = 0;

  while (i < len) {
    var tmp = chars[i];
    chars[i] = chars[len];
    chars[len] = tmp;
    i++;
    len--;
  }

  return Strings.concatAll(chars);
}

void main() {
  var s = "Hello , world";
  print(s);
  print(reverse(s));
}

(or)

String reverse(String s) {
  StringBuffer sb=new StringBuffer();
  for(int i=s.length-1;i>=0;i--) {
    sb.add(s[i]);
  }
  return sb.toString();
}

main() {
  print(reverse('Hello , world'));
}

Answer 3

There is a utils package that covers this function. It has some more nice methods for operation on strings.

Install it with :

dependencies:
  basic_utils: ^1.2.0

Usage :

String reversed = StringUtils.reverse("helloworld");

Github:

https://github.com/Ephenodrom/Dart-Basic-Utils

Answer 4

The library More Dart contains a light-weight wrapper around strings that makes them behave like an immutable list of characters:

import 'package:more/iterable.dart';

void main() {
  print(string('Hello World').reversed.join());
}

Answer 5

I've made a small benchmark for a few different alternatives:

String reverse0(String s) {
  return s.split('').reversed.join('');
}

String reverse1(String s) {
  var sb = new StringBuffer();
  for(var i = s.length - 1; i >= 0; --i) {
    sb.write(s[i]);
  }
  return sb.toString();
}

String reverse2(String s) {
  return new String.fromCharCodes(s.codeUnits.reversed);
}

String reverse3(String s) {
  var sb = new StringBuffer();
  for(var i = s.length - 1; i >= 0; --i) {
    sb.writeCharCode(s.codeUnitAt(i));
  }
  return sb.toString();
}

String reverse4(String s) {
  var sb = new StringBuffer();

  var i = s.length - 1;

  while (i >= 3) {
    sb.writeCharCode(s.codeUnitAt(i-0));
    sb.writeCharCode(s.codeUnitAt(i-1));
    sb.writeCharCode(s.codeUnitAt(i-2));
    sb.writeCharCode(s.codeUnitAt(i-3));
    i -= 4;
  }

  while (i >= 0) {
    sb.writeCharCode(s.codeUnitAt(i));
    i -= 1;
  }

  return sb.toString();
}

String reverse5(String s) {
  var length = s.length;
  var charCodes = new List(length);
  for(var index = 0; index < length; index++) {
    charCodes[index] = s.codeUnitAt(length - index - 1);
  }

  return new String.fromCharCodes(charCodes);
}
main() {
  var s = "Lorem Ipsum is simply dummy text of the printing and typesetting industry.";

  time('reverse0', () => reverse0(s));
  time('reverse1', () => reverse1(s));
  time('reverse2', () => reverse2(s));
  time('reverse3', () => reverse3(s));
  time('reverse4', () => reverse4(s));
  time('reverse5', () => reverse5(s));
}

Here is the result:

reverse0: => 331,394 ops/sec (3 us) stdev(0.01363)
reverse1: => 346,822 ops/sec (3 us) stdev(0.00885)
reverse2: => 490,821 ops/sec (2 us) stdev(0.0338)
reverse3: => 873,636 ops/sec (1 us) stdev(0.03972)
reverse4: => 893,953 ops/sec (1 us) stdev(0.04089)
reverse5: => 2,624,282 ops/sec (0 us) stdev(0.11828)

Answer 6

Here's one way to reverse an ASCII String in Dart:

input.split('').reversed.join('');

1. split the string on every character, creating an List
2. generate an iterator that reverses a list
3. join the list (creating a new string)

Note: this is not necessarily the fastest way to reverse a string. See other answers for alternatives.

Note: this does not properly handle all unicode strings.