/**
 * 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_07_FIter {

    static func FItera(n: Int) -> Int {
        var acc1: [Int] = Array<Int>()
        var nV = n
        while (nV != 0) {
            acc1.insert(nV, at:0)
            nV = nV - 1
        }
        var acc2: Int = 1
        var rev: ArraySlice<Int> = acc1[0 ... acc1.count-1]
        while (rev.count > 0) {
            let head = rev[rev.startIndex]
            acc2 = acc2 * head
            let rest = rev.suffix(from: rev.startIndex+1)
            rev = rest
        }
        return acc2
    }

    static func FTR(n: Int) -> Int  {
        func f(n: Int, acc: Int) -> Int {
            if (n == 0) {
                return acc
            } else {
                return f(n: n-1, acc: acc * n)
            }
        }
        return f(n: n, acc: 1)
    }

    static func FIter(n: Int) -> Int  {
        var f = 1
        var nV = n
        while (nV != 0) {
            let (n_, f_) = (nV-1, nV * f)
            nV = n_
            f = f_
        }
        return f
    }

    static func run() {
        print(FItera(n: 10))
        print(FTR(n: 10))
        print(FIter(n: 10))
    }

}