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    <p>In my test this is 75% to %90 faster than array sort with the same System.Func comparer. I use it to sort a custom struct. you can easily modify it to sort classes.</p> <pre><code>public class DualQuickSort&lt;T&gt; where T : struct { private readonly System.Func&lt;T, T, int&gt; comparer; public DualQuickSort(System.Func&lt;T, T, int&gt; comparer) { this.comparer = comparer; } public DualQuickSort(IComparer&lt;T&gt; comparer) : this(comparer.Compare) { } public void Sort(T[] a) { Sort(a, 0, a.Length); } public void Sort(T[] a, int fromIndex, int toIndex) { RangeCheck(a.Length, fromIndex, toIndex); DualPivotQuicksort(a, fromIndex, toIndex - 1, 3); } private static void RangeCheck(int length, int fromIndex, int toIndex) { if (fromIndex &gt; toIndex) { throw new ArgumentException("fromIndex &gt; toIndex"); } if (fromIndex &lt; 0) { throw new IndexOutOfRangeException(fromIndex + " is less than 0"); } if (toIndex &gt; length) { throw new IndexOutOfRangeException(toIndex + " is greater than " + fromIndex); } } private static void Swap(T[] a, int i, int j) { var temp = a[i]; a[i] = a[j]; a[j] = temp; } private void DualPivotQuicksort(T[] a, int left, int right, int div) { var len = right - left; if (len &lt; 27) { // insertion sort for tiny array for (var i = left + 1; i &lt;= right; i++) { for (var j = i; j &gt; left &amp;&amp; comparer(a[j] , a[j - 1])==-1; j--) { Swap(a, j, j - 1); } } return; } var third = len / div; // "medians" var m1 = left + third; var m2 = right - third; if (m1 &lt;= left) { m1 = left + 1; } if (m2 &gt;= right) { m2 = right - 1; } if (comparer(a[m1] , a[m2])==-1) { Swap(a, m1, left); Swap(a, m2, right); } else { Swap(a, m1, right); Swap(a, m2, left); } // pivots var pivot1 = a[left]; var pivot2 = a[right]; // pointers var less = left + 1; var great = right - 1; // sorting for (var k = less; k &lt;= great; k++) { if (comparer(a[k] , pivot1)==-1) { Swap(a, k, less++); } else if (comparer(a[k], pivot2) == 1) { while (k &lt; great &amp;&amp; comparer(a[great] , pivot2)==1) { great--; } Swap(a, k, great--); if (comparer(a[k], pivot1) == -1) { Swap(a, k, less++); } } } // Swaps var dist = great - less; if (dist &lt; 13) { div++; } Swap(a, less - 1, left); Swap(a, great + 1, right); // subarrays DualPivotQuicksort(a, left, less - 2, div); DualPivotQuicksort(a, great + 2, right, div); // equal elements if (dist &gt; len - 13 &amp;&amp; comparer(pivot1,pivot2)!=0) { for (int k = less; k &lt;= great; k++) { if (comparer(a[k] , pivot1)==0) { Swap(a, k, less++); } else if (comparer(a[k], pivot2) == 0) { Swap(a, k, great--); if (comparer(a[k], pivot1) == 0) { Swap(a, k, less++); } } } } // subarray if (comparer(pivot1 , pivot2)==-1) { DualPivotQuicksort(a, less, great, div); } } } </code></pre>
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    1. POWhat is the most elegant way of shell sorting (comb / diminishing increment sorting) in C#?
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    1. USGary
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      1. VTUpMod
    1. COThat range check is getting mighty famous these days ;)
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      1. USjoelittlejohn
 

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