It’s a very basic question: given two strings a and b, how would you swap their values?
static void Main(string[] args)
{
string a = "Some random string.";
string b = "Another one.";
// begin code
// end code
Console.WriteLine(a);
Console.WriteLine(b);
Console.ReadKey();
}
Fairly trivial, right? Still, there are a number of ways to do this.
The most basic one is the one everyone and their dog initially comes up with:
static void Main(string[] args)
{
string a = "Some random string.";
string b = "Another one.";
// begin code
string c = a;
a = b;
b = c;
// end code
Console.WriteLine(a);
Console.WriteLine(b);
Console.ReadKey();
}
But is this the most efficient way to do it? You might not like that extra string variable you had to declare there, so you might think, I can do this with less:
static void Main(string[] args)
{
string a = "Some random string.";
string b = "Another one.";
// begin code
int i = a.Length;
a = a + b;
b = a.Substring(0, i);
a = a.Substring(i);
// end code
Console.WriteLine(a);
Console.WriteLine(b);
Console.ReadKey();
}
Or with even less:
static void Main(string[] args)
{
string a = "Some random string.";
string b = "Another one.";
// begin code
a = a + b;
b = a.Substring(0, a.Length - b.Length);
a = a.Substring(b.Length);
// end code
Console.WriteLine(a);
Console.WriteLine(b);
Console.ReadKey();
}
But which one is more efficient? Well, I don’t know enough about the internals of the .NET framework to give an exact answer to this, but I wouldn’t be surprised if it’s the first one. The second example “only” declares an extra integer value, which on average would take less memory space than a string. The third example doesn’t declare any extra variables at all. But they do both modify a to hold both a and b. Let’s just count, shall we?
The first example at least requires space O(2a + 2b).
The second example requires O(i + 2a + 2b).
The third example again requires O(2a + 2b).
Between the first and the third examples, the first one creates a new string variable, but because of the immutability of strings in .NET, so does the third when it modifies a! Next, the third example has some substring operations while the first simply reassigns string values. So, is the “smart” solution the better one? Probably not in this case…