获取数组排序的索引

可以枚举数组,按元素对其排序,并映射元素偏移:

let array = [1,3,2,5,4]
let sortedIndices = array.enumerated()
                  .sorted{ $0.element < $1.element }
                  .map{ $0.offset }
sortedIndices   // [0, 2, 1, 4, 3]

如果愿意,还可以扩展集合并实现自己的方法,前提是将其元素约束到可比较的协议:

extension Collection where Element: Comparable {
    func sortedIndices() -> [Int] {
        return enumerated()
            .sorted{ $0.element < $1.element }
            .map{ $0.offset }
    }
}

let array = [1,3,2,5,4]
let sortedIndices = array.sortedIndices()
sortedIndices   // [0, 2, 1, 4, 3]

另一个选项是添加一个闭包作为参数,以允许通过以下方式进行排序:

extension Collection where Element: Comparable {
    func sortedIndices() -> [Int] {
        return sortedIndices(by: <)
    }
}
extension Collection {
    func sortedIndices(by condition: (Element, Element) -> Bool) -> [Int] {
        return enumerated()
            .sorted{ condition($0.element,$1.element) }
            .map{ $0.offset }
    }
}

let array = [1,3,2,5,4]
let sortedIndices = array.sortedIndices(by: >)
sortedIndices    // [3, 4, 1, 2, 0]