Recursion is recursion is recursion is recursion is recursion . . .

So, bought a book the other day, called "Introduction to Algorithms", which is a heavy, thick book that covers well, algorithms in computing, makes a case for them as a technology (it is not enough to have fast hardware, the instruction set must be efficient, as well), and goes on and on with tons of heavy calculus that I don't well, understand all that well. So far I've read up on insertion sort and merge sort, and, while I actually did make (read: copy) an insertion sort algorithm and make it work (correctly), I never did a merge sort.

See, the problem with recursion is that, its not very easy to see where its going. Yet, for some problems, recursion is the way to go. Take the game Portal and its view of looking through portals like in a mirror (It's really something better shown than explained... but the next time you see two mirrors directly opposite each other, its like that). They explain in the commentary that this is done recursively. And it makes sense. I couldn't see how it'd be doing using iterations.

Except... recursion is a type of loop. But a special type of loop. One that is actually very elegant and beautiful. It is also not all that verbose, compared to that of say a for loop or while loop.
// sorry about the lack of indents. Blogger doesn't like lots of spaces for some reason
Consider . . . (in Java syntax, at least. Well, I think this is correct. Merge sort isn't working but this is from the book)

merge (A, p, r) {
     if p < r) {
          q = (p + r) / 2;
          merge (A, p, q);
          merge (A, q + 1, r);
          merge (A, p, q, r);
    }
}

where the method merge (A, p, r) calls itself several times, breaks its problem down through both halves of the array and then reassembles the list in sorted order, which is what the last method does. At least, this is how I understand it.

Merge sort I do not actually have working. I have something, and by something I mean it sort of sorts an array and loses a huge chunk of data by the time its done. And why I don't know.

This is a lot more elegant than, say, the insertion sort with its for loop and while loop, although a bit harder to grasp. Merge sort, however, is quite efficient for large arrays.

Where was I going with this? Well, I just built a word-counter program that solves counting words line by line recursively. It reads in a line, takes out the first word, and calls itself with the new sentence. It's exit condition is satisfied when the line it is working with no longer contains a space.

It isn't perfect by any means. A long trail of spaces, or, say, a blank line will up the word count per space or per line. Putting in the wrong file name will terminate the program without any explanation as to why. That I need to fix. Maybe I could throw some other checks in there to make sure that the line doesn't contain nothing or doesn't count extra spaces. I mean, maybe that would be easy. But it means more steps, too.

But then computers are fast, anyway. No, I mean, seriously fast.