Optimize space

[Damonvvong]

No description provided.

[tonyarnold]

Interesting! Could you give me a really brief description of what your changes do?

[Damonvvong]

First of all，the k = x - y, so k is in [-M,N]
so I change the length of vertices to [0...M+N], it is -M...N in the whitepaper

reference

// before
var vertices = Array(repeating: -1, count: 2 * Int(max) + 1) // from [0...2*max], it is -max...max in the whitepaper
// after
var vertices = Array(repeating: -1, count: max + 1) // from [0...N+M], it is -M...N in the whitepaper

And then, I thing we should skip when the k is not in [-M,N]

guard k >= -toCount && k <= fromCount else {
    continue
}

last,I think force unwraps is not the good choose,so i change the ! to ??
reference

if traceType == .insertion {
    let x = traceStep.nextX!
    let x = traceStep.nextX ?? -1
    return Trace(from: Point(x: x, y: x - k - 1), to: Point(x: x, y: x - k), D: D)		              
} else {
    let x = traceStep.previousX! + 1
    let x = (traceStep.previousX ?? 0) + 1
    return Trace(from: Point(x: x - 1, y: x - k), to: Point(x: x, y: x - k), D: D)
}

@tonyarnold

[tonyarnold]

Thanks for the run down @Damonvvong - I was referring to the impact upon memory use, performance, etc. I should have been more specific in my language.

[Damonvvong]

Sorry, I don't konw what you want.
So, I close it ~

[tonyarnold]

Please accept my apologies, @Damonvvong - I was only interested in what functional changes there might be in performance and behaviour after merging your changes. I have not had time to properly review and run tests against what you've contributed yet.