c sharp programming

Sorted Dictionaries
The Framework provides two dictionary classes internally structured such that their
content is always sorted by key:
• SortedDictionary<TKey,TValue>
• SortedList<TKey,TValue>*
(In this section, we will abbreviate <TKey,TValue> to <,>.)
SortedDictionary<,> uses  a  red/black  tree:  a data  structure designed  to perform
consistently well in any insertion or retrieval scenario.
SortedList<,> is implemented internally with an ordered array pair, providing fast
retrieval (via a binary-chop search) but poor insertion performance (because existing
values have to be shifted to make room for a new entry).
SortedDictionary<,>  is much  faster than SortedList<,> at  inserting elements  in a
random sequence (particularly with large lists). SortedList<,>, however, has an ex-
tra ability: to access items by index as well as by key. With a sorted list, you can go
directly  to  the nth element  in  the  sorting  sequence  (via  the  indexer on  the Keys/
Values properties). To do the same with a SortedDictionary<,>, you must manually
enumerate over n items. (Alternatively, you could write a class that combines a sorted
dictionary with a list class.)
None  of  the  three  collections  allows  duplicate  keys  (as  is  the  case  with  all
dictionaries).
The  following  example  uses  reflection  to  load  all  the  methods  defined  in
System.Object  into  a  sorted  list keyed by name,  and  then  enumerates  their keys
and values:

var sorted = new SortedList <string, MethodInfo>();
foreach (MethodInfo m in typeof (object).GetMethods())
  sorted [m.Name] = m;
foreach (string name in sorted.Keys)
  Console.WriteLine (name);
foreach (MethodInfo m in sorted.Values)
  Console.WriteLine (m.Name + " returns a " + m.ReturnType);
Here’s the result of the first enumeration:
Equals
GetHashCode
GetType
ReferenceEquals
ToString
Here’s the result of the second enumeration:
Equals returns a System.Boolean
GetHashCode returns a System.Int32
GetType returns a System.Type
ReferenceEquals returns a System.Boolean
ToString returns a System.String
Notice that we populated the dictionary through its indexer. If we instead used the
Add method, it would throw an exception because the object class upon which we’re
reflecting overloads the Equals method, and you can’t add the same key twice to a
dictionary. By using  the  indexer,  the  later entry overwrites  the earlier entry, pre-
venting this error.

You can store multiple members of the same key by making each
value element a list:
SortedList <string, List<MethodInfo>>
Extending our example, the following retrieves the MethodInfo whose key is "GetHash
Code", just as with an ordinary dictionary:
Console.WriteLine (sorted ["GetHashCode"]);      // Int32 GetHashCode()
So  far, everything we’ve done would also work with a SortedDictionary<,>. The
following two lines, however, which retrieve the last key and value, work only with
a sorted list:
Console.WriteLine (sorted.Keys  [sorted.Count - 1]);            // ToString
Console.WriteLine (sorted.Values[sorted.Count - 1].IsVirtual);  // True