Monday, 14 December 2009

C# QuickSort using Continuation Passing Style (As requested by a comment)

using System;
using System.Linq;
using System.Collections.Generic;

public static class ListExtensions
    public static Tuple<IEnumerable<T>, IEnumerable<T>> Partition<T>(
         this IEnumerable<T> items, Func<T, bool> p)
        var xs = items.Where(p);
        var ys = items.Except(xs);
        return Tuple.Create(xs, ys);

    public static IEnumerable<T> Loop<T>(
        IEnumerable<T> xs,
        Func<IEnumerable<T>, IEnumerable<T>> cont) where T : IComparable
        if (!xs.GetEnumerator().MoveNext())
            return cont(new T[0]);
            var x = xs.First();
            var xsp = xs.Skip(1);
            var parts = xsp.Partition(y => y.CompareTo(x) > 0);
            return Loop<T>(parts.Item1, lacc =>
                   Loop<T>(parts.Item2, racc =>
                       cont(lacc.Concat(new[] { x }).Concat(racc))));

    public static IEnumerable<T> QuickSort<T>(this IEnumerable<T> xs)
                                 where T : IComparable
        return Loop<T>(xs, x => x);

1 comment:

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