多段階選抜 (VB)

' http://qiita.com/Nabetani/items/1c83005a854d2c6cbb69
' http://nabetani.sakura.ne.jp/hena/ord24eliseq/

imports System
imports System.Linq
imports System.Collections.Generic
'imports System.Runtime.InteropServices

module Hena24
    '<DllImport("c")>
    'private function cbrt(ByVal d as double) as double
    'end function

    private function isqrt(ByVal n as integer) as integer
        if n<=0
            return 0
        end if
        if n<4
            return 1
        end if
        dim x as integer=0
        dim y as integer=n
        while x<>y andalso x+1<>y
            x=y
            y=((n\y)+y)\2
        end while
        return x
    end function
    private function icbrt(ByVal n as integer) as integer
        if n<0
            return -icbrt(-n)
        end if
        if n=0
            return 0
        end if
        if n<8
            return 1
        end if
        dim x as integer=0
        dim y as integer=n
        while x<>y andalso x+1<>y
            x=y
            y=((n\y\y)+y*2)\3
        end while
        return x
    end function

    private function is_sq(ByVal n as integer) as boolean
        dim x as integer=isqrt(n)
        'cint(Math.Sqrt(n))
        return x*x=n
    end function

    private function is_cb(ByVal n as integer) as boolean
        dim x as integer=icbrt(n)
        'cint(cbrt(n))
        return x*x*x=n
    end function

    private function is_multiple(ByVal i as integer,ByVal n as integer) as boolean
        return i mod n=0
    end function
    private function is_le(ByVal i as integer,ByVal n as integer) as boolean
        return i<=n
    end function

    iterator function generate() as IEnumerable(of integer)
        dim i as integer=1
        while true
            yield i
            i+=1
        end while
    end function

    iterator function drop_prev(ByVal check as Func(of integer,boolean),ByVal _prev as IEnumerable(of integer)) as IEnumerable(of integer)
        dim prev as IEnumerator(of integer)=_prev.GetEnumerator()
        prev.MoveNext()
        dim a as integer=prev.Current
        prev.MoveNext()
        dim b as integer=prev.Current
        while true
            if not check(b)
                yield a
            end if
            a=b
            prev.MoveNext()
            b=prev.Current
        end while
    end function

    iterator function drop_next(ByVal check as Func(of integer,boolean),ByVal _prev as IEnumerable(of integer)) as IEnumerable(of integer)
        dim prev as IEnumerator(of integer)=_prev.GetEnumerator()
        prev.MoveNext()
        dim a as integer=prev.Current
        prev.MoveNext()
        dim b as integer=prev.Current
        yield a
        while true
            if not check(a)
                yield b
            end if
            a=b
            prev.MoveNext()
            b=prev.Current
        end while
    end function

    iterator function drop_n(ByVal check as Func(of integer,integer,boolean),ByVal n as integer,ByVal _prev as IEnumerable(of integer)) as IEnumerable(of integer)
        dim prev as IEnumerator(of integer)=_prev.GetEnumerator()
        dim i as integer=0
        while true
            i+=1
            prev.MoveNext()
            dim a as integer=prev.Current
            if not check(i,n)
                yield a
            end if
        end while
    end function

    sub Main()
        dim f as new Dictionary(of char,Func(of IEnumerable(of integer),IEnumerable(of integer))) from {
            {"S"c,Function(e) drop_next(addressof is_sq,e)},
            {"s"c,Function(e) drop_prev(addressof is_sq,e)},
            {"C"c,Function(e) drop_next(addressof is_cb,e)},
            {"c"c,Function(e) drop_prev(addressof is_cb,e)},
            {"h"c,Function(e) drop_n(addressof is_le,100,e)}
        }
        for i as integer=2 to 9
            dim j as integer=i
            f(chr(48+j)) = Function(e) drop_n(addressof is_multiple,j,e)
        next
        dim line as string=Console.ReadLine()
        while line isnot nothing
            dim first as boolean=true
            'cS => f("S"c)(f("c"c)(generate()))
            for each n as integer in line.Aggregate(generate(),Function(s,e) f(e)(s)).Take(10)
                if not first
                    Console.Write(","c)
                end if
                first=false
                Console.Write(n)
            next
            Console.WriteLine()
            Console.Out.Flush()
            line=Console.ReadLine()
        end while
    end sub
end module