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Generic Quick Sort using anonymous methods

, 22 Dec 2004
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Shows how to implement generic methods and how to use anonymous methods in C# 2.0.

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Introduction

The code simply implements static generic methods. It does not really solve any problems as there is a sort method in the framework that is probably better than this one. Its purpose is to show the quicksort algorithm and how to use generics and anonymous methods.

Using the code

To use this code, just pass any array and delegate method that can compare items in the array against each other. Notice that I use the keyword delegate as I define an anonymous method. The parameters and return type of this anonymous method (if any) must match the signature of the delegate type expected, in this case Compare.

using System;
using System.Text;

public class Test
{
    public delegate bool Compare<T>(T rhs, T lhs);
    public static void Main()
    {
        Random r = new Random();
        int[] stuff = new int[10];
        for (int i = 0; i < stuff.Length; i++)
            stuff[i] = r.Next(10);
        QuickSort(ref stuff, delegate(int rhs, int lhs){return rhs <= lhs; });
        Console.WriteLine(PrintArray(stuff, 0, stuff.Length));
    }
    public static void QuickSort<T>(ref T[] values, Compare<T> comp)
    {
        QuickSortRecurse(ref values, 0, values.Length, comp);
    }
    public static void Swap<T>(ref T a, ref T b)
    {
        T temp = a;
        a = b;
        b = temp;
    }
    public static string PrintArray<T>(T[] values, int start, int end)
    {
        StringBuilder builder = new StringBuilder();
        for (int i = start; i < end; i++)
        {
            builder.Append(values[i].ToString());
            builder.Append(" ");
        }
        return builder.ToString();
    }
    public static void QuickSortRecurse<T>(ref T[] values, 
           int start, int end, Compare<T> comp)
    {
        if ((end - start) < 2) return;
        if (((end - start) == 2)) 
        {
            if (!comp(values[start], values[end - 1]))
            {
                Swap(ref values[start], ref values[end-1]);
            }
            return;
        }
        int stop = end - 1;
        int i = start + 1;
        while (i < stop)
        {
            while (!comp(values[start], values[i]) && i < stop) i++;
            while (comp(values[start], values[stop]) && stop >= i) stop--;
            if (i < stop)
            {
                Swap(ref values[i], ref values[stop]);
            }
        }
        if (start < stop)
        {
            Swap(ref values[start], ref values[stop]);
        }
        if (start < stop-1)
            QuickSortRecurse(ref values, start, stop, comp);
        if (stop+1 < end)
            QuickSortRecurse(ref values, stop + 1, end, comp);
    }
}

Points of Interest

Generics, as shown in this example, will dynamically derive the type of T when not explicitly stated.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Doug Coburn

United States United States
No Biography provided

Comments and Discussions

 
GeneralKernighan and Plaugher's bug lives on Pinmembermdgray27-Dec-04 9:21 
GeneralRe: Kernighan and Plaugher's bug lives on PinsussAnonymous27-Jun-05 11:25 
GeneralRe: Kernighan and Plaugher's bug lives on PinmemberBoudino20-Oct-05 1:35 
GeneralRe: Kernighan and Plaugher's bug lives on Pinmembermdgray20-Oct-05 14:36 

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