获取周围坐标的最短代码是什么？

Question

我不喜欢我对surroundingPositions 的以下实现来获取围绕特定位置的 x 和 y 坐标，因为在我看来，它对于简单的意图来说太长了，而且它有一个厄运金字塔结构。

struct Position: CustomStringConvertible {

    let x, y: Int

    var surroundingPositions: [Position] {
        var surroundingPositions: [Position] = []
        for x in (self.x - 1)...(self.x + 1) {
            for y in (self.y - 1)...(self.y + 1) {
                if !(x == self.x && y == self.y) {
                    surroundingPositions.append(Position(x: x, y: y))
                }
            }
        }
        return surroundingPositions
    }

    var description: String {
        return "(\(x),\(y))"
    }

}

用法：

let testPosition = Position(x: 1, y: 1)
print(testPosition.surroundingPositions)
// Output: [(0,0), (0,1), (0,2), (1,0), (1,2), (2,0), (2,1), (2,2)]

实现相同（正确）结果的最短方法是什么？我在想map、filter、reduce等函数，但目前还没有找到合适的组合...

Answer 1

好吧，您总是可以对其进行硬编码。在这里，我对增量进行了硬编码，并为每个增量创建了一个新的 Position：

var surroundingPositionsHardcoded: [Position] {
    let deltas: [(Int, Int)] = [(-1, -1), (-1, 0), (-1, +1), (0, -1), (0, +1), (+1, -1), (+1, 0), (+1, +1)]
    return deltas.map { Position(x: x+$0.0, y: y+$0.1) }
}

或者，您可以使用map 计算增量。这还有一个额外的好处，就是您可以增加周围的距离。

var surroundingPositionsComputed: [Position] {
    let deltas = (-1...1).map { dx in (-1...1).map { dy in (dx, dy) } }
        .joined()
        .filter { $0.0 != 0 || $0.1 != 0 }
    return deltas.map { Position(x: x+$0.0, y: y+$0.1) }
}

Answer 2

由于您只查找相邻位置并且似乎对 x 或 y 没有限制，因此您可以保存一组 (x, y) 翻译，每个翻译将给定的 Position 映射到其 8 个不同的相邻位置之一那些。

struct Position: CustomStringConvertible {
    let x, y: Int

    // order of resulting neighbouring positions, given a position P
    // (1)  (2)  (3)
    // (4)  (P)  (5)
    // (6)  (7)  (8)
    private static let surroundingPositionsTranslations: [(x: Int, y: Int)] = [
        (-1, -1), (0, -1), (1, -1),
        (-1,  0),          (1,  0),
        (-1, -1), (0, -1), (1, -1)]

    var surroundingPositions: [Position] {
        return Position.surroundingPositionsTranslations
            .map { Position(x: x + $0.x, y: y + $0.y) }
    }

    var description: String {
        return "(\(x),\(y))"
    }
}

// Note that I've changed the order w.r.t. OP:s original code
// (modify the transfotmation above to modify the order)
let testPosition = Position(x: 1, y: 1)
print(testPosition.surroundingPositions)
// Output: [(0,0), (1,0), (2,0), (0,1), (2,1), (0,0), (1,0), (2,0)]