Practical numbers: Difference between revisions

=={{header|C#|CSharp}}==

<lang csharp>using System.Collections.Generic; using System.Linq; using static System.Console;

class Program {

static bool soas(int n, IEnumerable<int> f) {

if (n <= 0) return false; if (f.Contains(n)) return true;

switch(n.CompareTo(f.Sum())) { case 1: return false; case 0: return true;

case -1: var rf = f.Reverse().ToList(); var d = n - rf[0]; rf.RemoveAt(0);

return soas(d, rf) || soas(n, rf); } return true; }

static bool ip(int n) { var f = Enumerable.Range(1, n >> 1).Where(d => n % d == 0).ToList();

return Enumerable.Range(1, n - 1).ToList().TrueForAll(i => soas(i, f)); }

static void Main() {

int c = 0, m = 333; for (int i = 1; i <= m; i += i == 1 ? 1 : 2)

if (ip(i) || i == 1) Write("{0,3} {1}", i, ++c % 10 == 0 ? "\n" : "");

Write("\nFound {0} practical numbers between 1 and {1} inclusive.\n", c, m);

do Write("\n{0,5} is a{1}practical number.",

m = m < 500 ? m << 1 : m * 10 + 6, ip(m) ? " " : "n im"); while (m < 1e4); } }</lang>

{{out}}

<pre> 1 2 4 6 8 12 16 18 20 24

28 30 32 36 40 42 48 54 56 60

64 66 72 78 80 84 88 90 96 100

104 108 112 120 126 128 132 140 144 150

156 160 162 168 176 180 192 196 198 200

204 208 210 216 220 224 228 234 240 252

256 260 264 270 272 276 280 288 294 300

304 306 308 312 320 324 330

Found 77 practical numbers between 1 and 333 inclusive.

666 is a practical number.

6666 is a practical number.

66666 is an impractical number.</pre>

=={{header|Visual Basic .NET}}==

{{trans|C#}}

<lang vbnet>Imports System.Collections.Generic, System.Linq, System.Console

Module Module1

Function soas(ByVal n As Integer, ByVal f As IEnumerable(Of Integer)) As Boolean

If n <= 0 Then Return False Else If f.Contains(n) Then Return True

Select Case n.CompareTo(f.Sum())

Case 1 : Return False : Case 0 : Return True

Case -1 : Dim rf As List(Of Integer) = f.Reverse().ToList() : Dim D as Integer = n - rf(0)

rf.RemoveAt(0) : Return soas(d, rf) OrElse soas(n, rf)

End Select : Return true

End Function

Function ip(ByVal n As Integer) As Boolean

Dim f As IEnumerable(Of Integer) = Enumerable.Range(1, n >> 1).Where(Function(d) n Mod d = 0).ToList()

Return Enumerable.Range(1, n - 1).ToList().TrueForAll(Function(i) soas(i, f))

End Function

Sub Main()

Dim c As Integer = 0, m As Integer = 333, i As Integer = 1 : While i <= m

If ip(i) OrElse i = 1 Then c += 1 : Write("{0,3} {1}", i, If(c Mod 10 = 0, vbLf, ""))

i += If(i = 1, 1, 2) : End While

Write(vbLf & "Found {0} practical numbers between 1 and {1} inclusive." & vbLf, c, m)

Do : m = If(m < 500, m << 1, m * 10 + 6)

Write(vbLf & "{0,5} is a{1}practical number.", m, If(ip(m), " ", "n im")) : Loop While m < 1e4

End Sub

End Module</lang>

{{out}}

Same as C#