C# program to Generic Heap sort

 using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 using System.Text;  
 using System.Threading.Tasks;  
 using System.Security;  
 using System.Runtime.Versioning;  
 using System.Runtime.CompilerServices;  
 namespace sorting  
 {  
   class Sorting7  
   {  
     private static void Heapsort(T[] keys, int lo, int hi, IComparer<T> comparer)  
     {/*from w w w .j a v a 2s . c om*/  
       int n = hi - lo + 1;  
       for (int i = n / 2; i >= 1; --i)  
         ArraySortHelper<T>.DownHeap(keys, i, n, lo, comparer);  
       for (int index = n; index > 1; --index)  
       {  
         T[] a = keys;  
         int i = lo;  
         int num = index;  
         int j = i + num - 1;  
         Swap(a, i, j);  
         DownHeap(keys, 1, index - 1, lo, comparer);  
       }  
     }  
     private static void Swap(T[] a, int i, int j)  
     {  
       if (i == j)  
         return;  
       T obj = a[i];  
       a[i] = a[j];  
       a[j] = obj;  
     }  
     private static void DownHeap(T[] keys, int i, int n, int lo, IComparer<T> comparer)  
     {  
       T x = keys[lo + i - 1];  
       int num;  
       for (; i <= n / 2; i = num)  
       {  
         num = 2 * i;  
         if (num < n && comparer.Compare(keys[lo + num - 1], keys[lo + num]) < 0)  
           ++num;  
         if (comparer.Compare(x, keys[lo + num - 1]) < 0)  
           keys[lo + i - 1] = keys[lo + num - 1];  
         else  
           break;  
       }  
       keys[lo + i - 1] = x;  
     }  
   }  
 }