ReverseString.cs

using System.Text;
using System.Linq;
using BenchmarkDotNet.Attributes;

namespace Algorithms.ArraysAndStrings
{
    [MemoryDiagnoser]
    public class ReverseString
    {
        private const string INPUT = "Learning Algorithms";

        //Time: O(n)
        //Space: O(n)
        [Benchmark(Baseline = true)]
        [Arguments(INPUT)]
        public string FirstTry(string myEntireString)
        {
            StringBuilder reversedString = new StringBuilder(myEntireString.Length);

            for (int i = myEntireString.Length - 1; i >= 0; i--)
                reversedString.Append(myEntireString[i]);

            return reversedString.ToString();
        }

        //Time: O(n)
        //Space: O(n)
        [Benchmark]
        [Arguments(INPUT)]
        public string InJustOneLine(string myEntireString)
        {
            return string.Join("", myEntireString.ToCharArray().Reverse());
        }

        //Time: O(n)
        //Space: O(n)
        [Benchmark]
        [Arguments(INPUT)]
        public string InJustOneLine2(string myEntireString)
        {
            return new string(myEntireString.Reverse().ToArray());
        }

        //Time: O(n/2)
        //Space: O(n)
        [Benchmark]
        [Arguments(INPUT)]
        public string Fast(string myEntireString)
        {
            int halfSize = myEntireString.Length / 2;

            char[] reversedArray = new char[myEntireString.Length];

            for (int i = 0; i < halfSize; i++)
            {
                reversedArray[i] = myEntireString[myEntireString.Length - 1 - i];
                reversedArray[reversedArray.Length - 1 - i] = myEntireString[i];
            }

            if (halfSize % 2 != 0)
                reversedArray[halfSize] = myEntireString[halfSize];

            return new string(reversedArray);
        }

        [Benchmark]
        [Arguments(INPUT)]
        public string Vafzamora_Fast1(string myEntireString)
        {

            char[] reversedArray = myEntireString.ToCharArray();
            char buffer = ' ';

            for (int i = 0, j = myEntireString.Length - 1; i < myEntireString.Length / 2; i++, j--)
            {
                buffer = reversedArray[i];
                reversedArray[i] = reversedArray[j];
                reversedArray[j] = buffer;
            }

            return new string(reversedArray);
        }

        [Benchmark]
        [Arguments(INPUT)]
        public string Vafzamora_Fast2(string myEntireString)
        {

            char[] reversedArray = new char[myEntireString.Length];
            int middle = (myEntireString.Length / 2 + myEntireString.Length % 2);
            for (int i = 0, j = myEntireString.Length - 1; i < middle; i++, j--)
            {
                reversedArray[i] = myEntireString[j];
                reversedArray[j] = myEntireString[i];
            }

            return new string(reversedArray);
        }

        [Benchmark]
        [Arguments(INPUT)]
        public string Vafzamora_Obvious(string myEntireString)
        {

            char[] reversedArray = new char[myEntireString.Length];

            for (int i = myEntireString.Length - 1, j = 0; i >= 0; i--, j++)
            {
                reversedArray[j] = myEntireString[i];
            }

            return new string(reversedArray);
        }
    }
}