var str = "hhhhh   Hello playground"

extension String {
    static func groupBy(_ string: String, _ f: (Character, Character) -> Bool) -> [String] {
        let array = Array(string) as! [Character]
        let groups = Array.groupBy(array, f)
        return groups.map { g in String(g) }
    }

    static func group(_ string: String) -> [String] {
       return groupBy(string) { (leftChar, rightChar) in leftChar == rightChar }
    }
}

extension Array {
    static func groupBy(_ array: [Element] , _ f: (Element, Element) -> Bool) -> [[Element]] {
        guard let firstChar = array.first else {
            return []
        }
        let (left, right) = Array.span(array, { c in f(firstChar, c) })
        return [left] + groupBy(right, f)
    }


    static func span(_ array: [Element], _ pred: (Element) -> Bool) -> ([Element], [Element]) {
        if array.isEmpty {
            return ([], [])
        }
        let right = Array(array.drop(while: pred))
        let left = Array(array.prefix(while: pred))
        return (left, right)
    }

    func groupBy(_ f: (Element, Element) -> Bool) -> [[Element]] {
       return Array.groupBy(self, f)
    }
}

extension Array where Element: Equatable {
    static func group(_ array: [Element]) -> [[Element]] {
        return groupBy(array as! [Element]) { (leftElem, rightElem) in leftElem == rightElem }
    }

    func group() -> [[Element]] {
        return Array.group(self)
    }
}

let group = String.group(str)
print("Group string: \(group) \n")
let group1 = Array.group([1,2,5,5,5,6,7,7])
print("Group array: \(group1)\n")
let span1 = Array.span([1,1,1,2,2,2], { e in e != 2} )
print("Span array: \(span1)")