Task: Sorting algorithms_Quicksort
C#: 




#define Tripartite

namespace RosettaCode {
  using System;
  using System.Diagnostics;

  public class QuickSort<T> where T : IComparable {
    #region Constants
    public const UInt32 INSERTION_LIMIT_DEFAULT = 12;
    private const Int32 SAMPLES_MAX = 19;
    #endregion

    #region Properties
    public UInt32 InsertionLimit { get; }
    private T[] Samples { get; }
    private Int32 Left { get; set; }
    private Int32 Right { get; set; }
    private Int32 LeftMedian { get; set; }
    private Int32 RightMedian { get; set; }
    #endregion

    #region Constructors
    public QuickSort(UInt32 insertionLimit = INSERTION_LIMIT_DEFAULT) {
      this.InsertionLimit = insertionLimit;
      this.Samples = new T[SAMPLES_MAX];
    }
    #endregion

    #region Sort Methods
    public void Sort(T[] entries) {
      Sort(entries, 0, entries.Length - 1);
    }

    public void Sort(T[] entries, Int32 first, Int32 last) {
      var length = last + 1 - first;
      while (length > 1) {
        if (length < InsertionLimit) {
          InsertionSort<T>.Sort(entries, first, last);
          return;
        }

        Left = first;
        Right = last;
        var median = pivot(entries);
        partition(median, entries);
        

        var leftLength = Right + 1 - first;
        var rightLength = last + 1 - Left;

        
        
        
        
        if (leftLength < rightLength) {
          Sort(entries, first, Right);
          first = Left;
          length = rightLength;
        }
        else {
          Sort(entries, Left, last);
          last = Right;
          length = leftLength;
        }
      }
    }

    
    private static Int32 sampleSize(Int32 length, Int32 max = SAMPLES_MAX) {
      var logLen = (Int32)Math.Log10(length);
      var samples = Math.Min(2 * logLen + 1, max);
      return Math.Min(samples, length);
    }

    
    
    private T pivot(T[] entries) {
      var length = Right + 1 - Left;
      var samples = sampleSize(length);
      
      for (var sample = 0; sample < samples; sample++) {
        
        var index = (Int64)length * sample / samples + Left;
        Samples[sample] = entries[index];
      }

      InsertionSort<T>.Sort(Samples, 0, samples - 1);
      return Samples[samples / 2];
    }

    private void partition(T median, T[] entries) {
      var first = Left;
      var last = Right;
#if Tripartite
      LeftMedian = first;
      RightMedian = last;
#endif
      while (true) {
        
        
        
        while (median.CompareTo(entries[Left]) > 0) Left++;
        while (median.CompareTo(entries[Right]) < 0) Right--;

        
        if (Right <= Left) break;

        Swap(entries, Left, Right);
        swapOut(median, entries);
        Left++;
        Right--;
        
      }

      if (Left == Right) {
        Left++;
        Right--;
      }
      
      swapIn(entries, first, last);

      
      
    }
    #endregion

    #region Swap Methods
    [Conditional("Tripartite")]
    private void swapOut(T median, T[] entries) {
      if (median.CompareTo(entries[Left]) == 0) Swap(entries, LeftMedian++, Left);
      if (median.CompareTo(entries[Right]) == 0) Swap(entries, Right, RightMedian--);
    }

    [Conditional("Tripartite")]
    private void swapIn(T[] entries, Int32 first, Int32 last) {
      
      while (first < LeftMedian) Swap(entries, first++, Right--);
      while (RightMedian < last) Swap(entries, Left++, last--);
    }

    
    public void Swap(T[] entries, Int32 left, Int32 right) {
      Swap(ref entries[left], ref entries[right]);
    }

    
    public static void Swap(ref T e1, ref T e2) {
      var e = e1;
      e1 = e2;
      e2 = e;
    }
    #endregion
  }

  #region Insertion Sort
  static class InsertionSort<T> where T : IComparable {
    public static void Sort(T[] entries, Int32 first, Int32 last) {
      for (var next = first + 1; next <= last; next++)
        insert(entries, first, next);
    }

    
    private static void insert(T[] entries, Int32 first, Int32 next) {
      var entry = entries[next];
      while (next > first && entries[next - 1].CompareTo(entry) > 0)
        entries[next] = entries[--next];
      entries[next] = entry;
    }
  }
  #endregion
}

VB: Public Sub Quick(a() As Variant, last As Integer)

Dim aLess() As Variant
Dim aEq() As Variant
Dim aGreater() As Variant
Dim pivot As Variant
Dim naLess As Integer
Dim naEq As Integer
Dim naGreater As Integer

If last > 1 Then
    
    pivot = a(Int((last + 1) / 2))
    
    naLess = 0
    naEq = 0
    naGreater = 0
    For Each el In a()
      If el > pivot Then
        naGreater = naGreater + 1
        ReDim Preserve aGreater(1 To naGreater)
        aGreater(naGreater) = el
      ElseIf el < pivot Then
        naLess = naLess + 1
        ReDim Preserve aLess(1 To naLess)
        aLess(naLess) = el
      Else
        naEq = naEq + 1
        ReDim Preserve aEq(1 To naEq)
        aEq(naEq) = el
      End If
    Next
    
    Quick aLess(), naLess
    Quick aGreater(), naGreater
    
    P = 1
    For i = 1 To naLess
      a(P) = aLess(i): P = P + 1
    Next
    For i = 1 To naEq
      a(P) = aEq(i): P = P + 1
    Next
    For i = 1 To naGreater
      a(P) = aGreater(i): P = P + 1
    Next
End If
End Sub

Public Sub QuicksortTest()
Dim a(1 To 26) As Variant

 
 For i = 1 To 26: a(i) = 26 - i: Next
 Quick a(), 26
 For i = 1 To 26: Debug.Print a(i);: Next
 Debug.Print
 
 For i = 1 To 26: a(i) = Chr$(Asc("z") + 1 - i) & "-stuff": Next
 Quick a(), 26
 For i = 1 To 26: Debug.Print a(i); " ";: Next
 Debug.Print
End Sub