I had to write a string reverse function today and wasn't happy with my initial (basic) function so I
posted it on Stack Overflow to see what other algorithms that developers might come up with. My restriction was that it had to be in C# 2.0 and so I couldn't use LINQ. Out of curiosity I decided to do a performance test on each of the functions and while I was at it I threw in the LINQ equivalent to see how it would perform. For the test of a 500 character string I looped each function 100,000 times and for the test of a 10 character string I looped the functions 10,000,000 times.
These are the functions that I tested:
// string concatenation with for loop
public string ReverseA(string text)
{
char[] cArray = text.ToCharArray();
string reverse = String.Empty;
for (int i = cArray.Length - 1; i > -1; i--)
{
reverse += cArray[i];
}
return reverse;
}
// Array.Reverse function
public string ReverseB(string text)
{
char[] charArray = text.ToCharArray();
Array.Reverse(charArray);
return new string(charArray);
}
// push/pop Stack<>
public string ReverseC(string text)
{
Stack
resultStack = new Stack();
foreach (char c in text)
{
resultStack.Push(c);
}
StringBuilder sb = new StringBuilder();
while (resultStack.Count > 0)
{
sb.Append(resultStack.Pop());
}
return sb.ToString();
}
// LINQ
public string ReverseD(string text)
{
return new string(text.ToCharArray().Reverse().ToArray());
}
// StringBuilder
public string ReverseE(string text)
{
char[] cArray = text.ToCharArray();
StringBuilder reverse = new StringBuilder();
for (int i = cArray.Length - 1; i > -1; i--)
{
reverse.Append(cArray[i]);
}
return reverse.ToString();
}
What surprised me was how poorley LINQ did on the short string compared to the others.
You may also find the rudimentary test harness that I put together interesting:
delegate string ReverseDelegate(string text);
public void RunPerformance()
{
int loopCount = 10000000;
int stringSize = 100;
string[] reverseTextArray = Enumerable.Repeat
("abcde", stringSize).ToArray();
string reverseText = String.Join("", reverseTextArray);
// reverseText = "1234567890";
DateTime startTime, endTime;
ReverseDelegate[] reverseFunc = new ReverseDelegate[5];
reverseFunc[0] = ReverseA;
reverseFunc[1] = ReverseB;
reverseFunc[2] = ReverseC;
reverseFunc[3] = ReverseD;
reverseFunc[4] = ReverseE;
AssertThatFunctionsWorkCorrectly(reverseFunc);
TimeSpan[] reverseTime = new TimeSpan[reverseFunc.Length];
for (int i = 0; i < reverseFunc.Length; i++)
{
startTime = DateTime.Now;
for (int j = 0; j < loopCount; j++)
{
reverseFunc[i](reverseText);
}
endTime = DateTime.Now;
reverseTime[i] = endTime - startTime;
Console.WriteLine("{0}/{2} took {1}", i, reverseTime[i], reverseFunc[i].Method);
}
Console.WriteLine("break point");
}
private void AssertThatFunctionsWorkCorrectly(ReverseDelegate[] reverseFunc)
{
string test = "abcdefghi";
string expected = "ihgfedcba";
for(int i=0; i
