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C# Reverse String

Reverse the order of the characters in a string. Use ToCharArray and Array.Reverse.

Reverse string.

A string can be reversed. A reversal method can be implemented in several ways. Some ways are faster than others.Strings

And some methods

use more lines of code—they are more complex to understand. We review and time some string reversal methods with a recent .NET Framework.

An example.

This solution requires just 3 lines of code. The method shown in this article is based on my work with ToCharArray. It is static because it stores no state.ToCharArray

ReverseString: This method receives a string parameter—this is the string in which you wish to reverse the order of the letters.

Reverse: The method calls Array.Reverse to modify the order of the chars. Reverse cannot be used on a string directly.

StaticArray.Reverse

ToCharArray: The method copies to an array using ToCharArray. It returns a string with the new string constructor.

Char ArrayString Constructor
C# program that reverses strings using System; static class StringHelper { /// <summary> /// Receives string and returns the string with its letters reversed. /// </summary> public static string ReverseString(string s) { char[] arr = s.ToCharArray(); Array.Reverse(arr); return new string(arr); } } class Program { static void Main() { Console.WriteLine(StringHelper.ReverseString("framework")); Console.WriteLine(StringHelper.ReverseString("samuel")); Console.WriteLine(StringHelper.ReverseString("example string")); } } Output krowemarf leumas gnirts elpmaxe

Benchmark, string reversal.

Suppose your program must reverse strings millions or billions of times. Can we use some simple logic to optimize string reversal? Here we test 2 methods.

Method 1: This method uses ToCharArray and Array.Reverse. It is short and simple, probably good enough for most programs.

Method 2: This version allocates an empty char array, and iterates backwards through the string and assigns elements in the array.

Result: The iterative method ReverseStringDirect is faster—nearly twice as fast. It does not use Array.Reverse or ToCharArray.

C# program that benchmarks string reverse methods using System; using System.Diagnostics; class Program { public static string ReverseString(string s) { char[] array = s.ToCharArray(); Array.Reverse(array); return new string(array); } public static string ReverseStringDirect(string s) { char[] array = new char[s.Length]; int forward = 0; for (int i = s.Length - 1; i >= 0; i--) { array[forward++] = s[i]; } return new string(array); } static void Main() { int sum = 0; const int _max = 10000000; Console.WriteLine(ReverseString("test")); Console.WriteLine(ReverseStringDirect("test")); // Version 1: reverse with ToCharArray. var s1 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { sum += ReverseString("programmingisfun").Length; } s1.Stop(); // Version 2: reverse with iteration. var s2 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { sum += ReverseStringDirect("programmingisfun").Length; } s2.Stop(); Console.WriteLine(s1.Elapsed.TotalMilliseconds); Console.WriteLine(s2.Elapsed.TotalMilliseconds); } } Output tset tset 597.2342 ms ReverseString 392.2862 ms ReverseStringDirect

For optimal performance,

use caching. Also consider just iterating through a string backwards instead of ever creating a string. These approaches are always going to be fastest.

A summary.

We saw a method that receives a string and returns the string with its characters in the reverse order. It is one of many examples of using char arrays for string manipulation.
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