Fix initial threashold for k!=10,100,1000

[amallia]

Initial threashold is not set correctly is k is not 10,100 or 1000

[JMMackenzie]

This looks fine, but would it be preferable to use the next highest score if one exists?

For example, a user wants $k = 50$ - can't we use the 100 threshold?

[elshize]

Could be:

Self::map_kth_value(k).map(|idx| self.kth_score[idx]).unwrap_or(0)

But to @JMMackenzie's point, I think he means something like this:

pub fn kth(&self, k: usize) -> u8 {
    if k <= 1000 {
        self.kth_score[(k - 1).ilog10()]
    } else {
        0
    }
}

Notice I used log to make it succinct, but I would encourage you to benchmark if this makes sense.

Either way, even if you are using match/if, I wouldn't use map_kth_value, just straight up use a match statement and put self.kth_score[...] in each branch. The reason is that you'll need to do another check for Option, and then range check for array access. If anything, I would use self.kth_score.get(map_kth_value(k)).unwrap_or(0) and let the result of the inner func go out of range. This way, you should be able to only have one check, I think.

In fact, the function I suggested above could be:

pub fn kth(&self, k: usize) -> u8 {
    self.kth_score.get((k - 1).ilog10()).unwrap_or(0)
}

Though now you must calculate log first, even for large k. But if this is not an issue, you can hardly beat the simplicity of a one-liner ;)

[elshize]

Or how about this crazy idea:

pub fn kth(&self, k: usize) -> u8 {
    let idx = ((n > 10) as usize)
        + (n > 100) as usize
        + (n > 1000) as usize;
    self.kth_score.get(idx).unwrap_or(0)
}

[JMMackenzie]

That's beautiful 😍