Friday Programming Quiz [modified]

[David Stone]

So do I, honestly. :-D Anybody with VS and the May LINQ CTP installed want to try it out?

Once you wanted revolution
Now you're the institution
How's it feel to be the man?

[Judah Gabriel Himango]

I thought about a couple solutions. Most of the options are either compact and poor performance, or verbose and high performance. Here's one compact solution:

string GetIntersection(string csvString1, string csvString2)
{
foreach (string str in csvString2.Split(','))
if (!csvString1.Contains("," + str + ",") && !csvString1.EndsWith(str))
csvString1 += "," + str;

 return csvString1;

}

Of course, I'd never write code like that as it's hugely inefficient due to the excessive string concatenation. You could make a more efficient version with a StringBuilder, char array, or List of strings, but they'd be more verbose. :)

Tech, life, family, faith: Give me a visit. I'm currently blogging about: God-as-Judge, God-as-Forgiver The apostle Paul, modernly speaking: Epistles of Paul Judah Himango

[jesarg]

Your code will return false positives if csvString1 has element "hi" and csvString2 has element "hide".

[David Stone]

J.Doli wrote:

I couldnt find List<>.Intersect() anywhere on MSDN

It's not there yet. You only get List<T>.Intersect() if you install the LINQ CTPs.

Oh geez... the forum keeps spinning... you'll take care o f it i'm sure, c'ause ... yeah, i neede this. *cough* anyway good job finding the bug.
-Shog9 on...a Firefox bug.

[Lost User]

thanks for pointing that out. Here is my next try. public string GetIntersection(string csvString1, string csvString2) { List stringList = new List(csvString2.Split(new char[] { ',' })); List results = new List(); foreach (string str in csvString1.Split(new char[] { ',' })) { if (stringList.Contains(str)) { results.Add(str); } } return String.Join(",", results.ToArray()); } I dont like it that much, i just keep thinking that there is a better way.

[David Stone]

It won't. Also, my string splitting is wrong. I've modified it with the correct answer.

Oh geez... the forum keeps spinning... you'll take care o f it i'm sure, c'ause ... yeah, i neede this. *cough* anyway good job finding the bug.
-Shog9 on...a Firefox bug.

[Ennis Ray Lynch Jr]

Sue me, I am lazy and uncreative right now. StringBuilder sb = new StringBuilder(); Hashtable table = new Hashtable(); string[] splitList = csvString1.Split(new char[]{','}); foreach(string s in splitList){ table[s] = s; } splitList = csvString2.Split(new char[]{','}); foreach(string s in splitList){ table[s] = s; } foreach(string s in table.Values){ sb.Append(s); } return sb.ToString();

---

On two occasions I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. - Charles Babbage

[Matt Gerrans]

Yeah. You need to get a smaller monitor. Your team will thank you. BTW: "but at least it works" is a commonly used rationale (or excuse) for code that usually doesn't work very well at all. Remember, good code is about readability too. If it wasn't for that, we wouldn't keep source code after it was compiled once. Code is for people, not computers. All computers care about is the machine instructions.

Matt Gerrans

[Joe Woodbury]

For the heck of it I threw together a C++ version. Note that the CMTrieIntT class is one of my own implementations of a trie and is extremely fast. (I have a case insensitive version that could also be used.)

int GetString(LPCTSTR& pStr)
{
	while (*pStr == ',')
		pStr++;

	int len = 0;

	while (pStr[len] && pStr[len] != ',')
		len++;

	return len;
}

CString GetIntersection(LPCTSTR pStr1, LPCTSTR pStr2)
{
	CMTrieIntT trie;

	for ( ; ; )
	{
		int len = GetString(pStr1);
		if (len == 0)
			break;

		trie.Add(pStr1, 0, len);

		pStr1 += len;
	}

	CString rval;

	for ( ; ; )
	{
		int len = GetString(pStr2);
		if (len == 0)
			break;

		if (trie.KeyExists(pStr2, len))
		{
			if (rval.GetLength() > 0)
				rval += ',';

			rval.Append(pStr2, len);
		}

		pStr2 += len;
	}

	return rval;
}

Anyone who thinks he has a better idea of what's good for people than people do is a swine. - P.J. O'Rourke

[Henrik Husted]

my $l1 = "cat,rat,dog,lion"; my $l2 = "lion,elephant,mouse,tiger,rat,dog"; my (%h1,%h2); foreach(split ",", $l1) { $h1{$_}=$_;} foreach(split ",", $l2) { $h2{$_}=$_;} foreach( sort keys %h1 ) { if( $h2{$_} ) { print "$h1{$_}\n"; } }

[Marc Clifton]

Why use Regex.Split instead of just csv1.Split(',') ? Marc

Thyme In The Country

People are just notoriously impossible. --DavidCrow
There's NO excuse for not commenting your code. -- John Simmons / outlaw programmer
People who say that they will refactor their code later to make it "good" don't understand refactoring, nor the art and craft of programming. -- Josh Smith

[David Stone]

Because Regex.Split takes a String. String.Split needs a char array. And so I didn't want to construct a whole char[]. ;P There's no other good reason.

---

Mandrake, do you realize that in addition to fluoridating water, why, there are studies underway to fluoridate salt, flour, fruit juices, soup, sugar, milk, ice cream. Ice cream, Mandrake. Children's ice cream.

[Marc Clifton]

David Stone wrote:

String.Split needs a char array.

Obviously, the documentation and Intellisense does not match the implementation, as:

            string foo="a,b,c";
            string\[\] foo2=foo.Split(',');

Compiles fine. Unless there's some implicit conversion to char[]? I use the above syntax all the time! :~ Marc

Thyme In The Country

People are just notoriously impossible. --DavidCrow
There's NO excuse for not commenting your code. -- John Simmons / outlaw programmer
People who say that they will refactor their code later to make it "good" don't understand refactoring, nor the art and craft of programming. -- Josh Smith

[David Stone]

Weird. Huh. Then there's really no reason (here) to use Regex.Split. Go figure.

Oh geez... the forum keeps spinning... you'll take care o f it i'm sure, c'ause ... yeah, i neede this. *cough* anyway good job finding the bug.
-Shog9 on...a Firefox bug.