Binary Search IList - CSharp System.Collections.Generic

Description

Binary Search IList

Demo Code

using System.Linq;
using System.Collections.Generic;
using System.Collections;
using System;//from   ww w .  j  a va2  s  .  co  m

public class Main{
        // http://stackoverflow.com/questions/1766328/can-linq-use-binary-search-when-the-collection-is-ordered
      public static T BinarySearch<T, TKey>(this IList<T> list, Func<T, TKey> keySelector, TKey key)
      where TKey : IComparable<TKey>
      {
         int min = 0;
         int max = list.Count;
         while (min < max)
         {
            int mid = (max + min) / 2;
            T midItem = list[mid];
            TKey midKey = keySelector(midItem);
            int comp = midKey.CompareTo(key);
            if (comp < 0)
            {
               min = mid + 1;
            }
            else if (comp > 0)
            {
               max = mid - 1;
            }
            else
            {
               return midItem;
            }
         }
         if (min == max &&
            keySelector(list[min]).CompareTo(key) == 0)
         {
            return list[min];
         }

         throw new InvalidOperationException("Item not found");
      }
}

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