I made some comment to Kris recently about how I wish I had more formal computer science training. I took all of two programming classes in college, and learned the rest on my own. I believe I do okay, since programming is essentially solving one big logic problem, but every so often I solve a problem with brute force instead of creating an elegant solution.
Kris offered to help me out with the formal computer science education, and suggested we go through his Algorithms book. I agreed, figuring it would happen not before next year, given all of my copious free time.
When I was at Hackday yesterday, Kris pinged me and asked if PHP could handle recursion, which cracked me up (the answer being, uh, yes, of course). When I said yes, he asked me if I could write a recursive function that printed out a series of numbers, from one to the single function argument N. The two keys to this problem were recursion and single parameter.
Counting down from N to 1 was easy. I figure both are easy, but counting down is clearly the easier:
function kris($n = 1) {
print "$n ";
if ($n > 1) {
kris($n - 1);
}
}
Oddly enough, counting up was harder for me. I told Kris he couldn't offer any hints, and eventually I figured out a convoluted solution using a static variable. My solution clearly showed me my lack of CS education. Kris' solution was much simpler:
function kitt($n=1) {
if ($n>1) {
kitt($n-1);
}
print "$n ";
}
As Kris commented, people forget you can do the recursion first, and the action second, when writing recursive functions.
A candidate at Kris' work was unable to solve the problem, and he wanted to see if I could, especially since I was commenting on the CS education I didn't have. I did solve it, but not correctly.
Next time, I'll have the trick. This time? I felt like an idiot.
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