/**
 * Beispiel aus
 *
 * - Algorithmen und Datenstrukturen für Dummies
 *   - von Andreas Gogol-Döring und Thomas Letschert
 *   - Verlag Wiley-VCH; Oktober 2019
 *  - Kapitel 3, Daten und ihre Struktur
 *
 * @author A. Gogol-Döring, Th. Letschert
 */

import Foundation

struct AuD_03_05_ListSum {

    enum IntList {
        case Nil
        indirect case Cons (head: Int, tail: IntList)
    }

    static func FLst(n: Int) -> IntList {
        func F(x: Int) -> Int {
            return (x == 0) ? 1 : x * F(x: x - 1)
        }

        var l: IntList = IntList.Nil
        for i in 0...n {
            l = IntList.Cons(head: F(x: i), tail: l)
        }
        return l
    }

    static func ListSum(lst: IntList) -> Int {
        var s = 0
        var lstVar: IntList = lst
        whileLoop: while (true) {
            switch lstVar {
            case .Cons(let v, let rest) :
                s = s + v
                lstVar = rest
            case .Nil :
                break whileLoop
            }
        }
        return s
    }

    static func ListSumR(lst: IntList) -> Int {
        switch lst {
        case .Nil :
            return 0
        case .Cons(let v, let rest) :
            return v + ListSumR(lst: rest)
        }
    }

    static func run() {
        let l = IntList.Cons(head: 1, tail: .Cons(head: 2, tail: .Cons(head: 3, tail: .Cons(head: 4, tail: .Cons(head: 5, tail: .Nil)))))
        print(ListSum(lst: l))
        print(ListSumR(lst: l))
    }

}