List<T>.BinarySearch Method (T, IComparer<T>)

Parameters

• item
  Type: T
  The object to locate. The value can be nulla null reference (Nothing in Visual Basic) for reference types.

• comparer
  Type: System.Collections.Generic.IComparer<T>
  The IComparer<T> implementation to use when comparing elements.
  -or-
  nulla null reference (Nothing in Visual Basic) to use the default comparer Comparer<T>.Default.

Return Value

Type: System.Int32
The zero-based index of item in the sorted List<T>, if item is found; otherwise, a negative number that is the bitwise complement of the index of the next element that is larger than item or, if there is no larger element, the bitwise complement of Count.

Imports System.Collections.Generic

Public Class DinoComparer
   Implements IComparer(Of String)

   Public Function Compare(ByVal x As String, _
       ByVal y As String) As Integer _
       Implements IComparer(Of String).Compare

      If x Is Nothing Then
         If y Is Nothing Then
            ' If x is Nothing and y is Nothing, they're
            ' equal. 
            Return 0
         Else
            ' If x is Nothing and y is not Nothing, y
            ' is greater. 
            Return -1
         End If
      Else
         ' If x is not Nothing...
         '
         If y Is Nothing Then
            ' ...and y is Nothing, x is greater.
            Return 1
         Else
            ' ...and y is not Nothing, compare the 
            ' lengths of the two strings.
            '
            Dim retval As Integer = _
                x.Length.CompareTo(y.Length)

            If retval <> 0 Then
               ' If the strings are not of equal length,
               ' the longer string is greater.
               '
               Return retval
            Else
               ' If the strings are of equal length,
               ' sort them with ordinary string comparison.
               '
               Return x.CompareTo(y)
            End If
         End If
      End If
   End Function
End Class

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim dinosaurs As New List(Of String)
      dinosaurs.Add("Pachycephalosaurus")
      dinosaurs.Add("Amargasaurus")
      dinosaurs.Add("Mamenchisaurus")
      dinosaurs.Add("Deinonychus")
      Display(outputBlock, dinosaurs)

      Dim dc As New DinoComparer

      outputBlock.Text &= vbLf & "Sort with alternate comparer:" & vbCrLf
      dinosaurs.Sort(dc)
      Display(outputBlock, dinosaurs)

      SearchAndInsert(outputBlock, dinosaurs, "Coelophysis", dc)
      Display(outputBlock, dinosaurs)

      SearchAndInsert(outputBlock, dinosaurs, "Oviraptor", dc)
      Display(outputBlock, dinosaurs)

      SearchAndInsert(outputBlock, dinosaurs, "Tyrannosaur", dc)
      Display(outputBlock, dinosaurs)

      SearchAndInsert(outputBlock, dinosaurs, Nothing, dc)
      Display(outputBlock, dinosaurs)
   End Sub

   Private Shared Sub SearchAndInsert(ByVal outputBlock As System.Windows.Controls.TextBlock, _
       ByVal lis As List(Of String), _
       ByVal insert As String, ByVal dc As DinoComparer)

      outputBlock.Text &= String.Format(vbLf & _
          "BinarySearch and Insert ""{0}"":", insert) & vbCrLf

      Dim index As Integer = lis.BinarySearch(insert, dc)

      If index < 0 Then
         index = index Xor -1
         lis.Insert(index, insert)
      End If
   End Sub

   Private Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal lis As List(Of String))
      outputBlock.Text &= vbCrLf
      For Each s As String In lis
         outputBlock.Text &= s & vbCrLf
      Next
   End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'Sort with alternate comparer:
'
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Coelophysis":
'
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Oviraptor":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Tyrannosaur":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "":
'
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus

using System;
using System.Collections.Generic;

public class DinoComparer : IComparer<string>
{
   public int Compare(string x, string y)
   {
      if (x == null)
      {
         if (y == null)
         {
            // If x is null and y is null, they're
            // equal. 
            return 0;
         }
         else
         {
            // If x is null and y is not null, y
            // is greater. 
            return -1;
         }
      }
      else
      {
         // If x is not null...
         //
         if (y == null)
         // ...and y is null, x is greater.
         {
            return 1;
         }
         else
         {
            // ...and y is not null, compare the 
            // lengths of the two strings.
            //
            int retval = x.Length.CompareTo(y.Length);

            if (retval != 0)
            {
               // If the strings are not of equal length,
               // the longer string is greater.
               //
               return retval;
            }
            else
            {
               // If the strings are of equal length,
               // sort them with ordinary string comparison.
               //
               return x.CompareTo(y);
            }
         }
      }
   }
}

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      List<string> dinosaurs = new List<string>();
      dinosaurs.Add("Pachycephalosaurus");
      dinosaurs.Add("Amargasaurus");
      dinosaurs.Add("Mamenchisaurus");
      dinosaurs.Add("Deinonychus");
      Display(outputBlock, dinosaurs);

      DinoComparer dc = new DinoComparer();

      outputBlock.Text += "\nSort with alternate comparer:" + "\n";
      dinosaurs.Sort(dc);
      Display(outputBlock, dinosaurs);

      SearchAndInsert(outputBlock, dinosaurs, "Coelophysis", dc);
      Display(outputBlock, dinosaurs);

      SearchAndInsert(outputBlock, dinosaurs, "Oviraptor", dc);
      Display(outputBlock, dinosaurs);

      SearchAndInsert(outputBlock, dinosaurs, "Tyrannosaur", dc);
      Display(outputBlock, dinosaurs);

      SearchAndInsert(outputBlock, dinosaurs, null, dc);
      Display(outputBlock, dinosaurs);
   }

   private static void SearchAndInsert(System.Windows.Controls.TextBlock outputBlock, List<string> list,
       string insert, DinoComparer dc)
   {
      outputBlock.Text += String.Format("\nBinarySearch and Insert \"{0}\":", insert) + "\n";

      int index = list.BinarySearch(insert, dc);

      if (index < 0)
      {
         list.Insert(~index, insert);
      }
   }

   private static void Display(System.Windows.Controls.TextBlock outputBlock, List<string> list)
   {
      outputBlock.Text += "\n";
      foreach (string s in list)
      {
         outputBlock.Text += s + "\n";
      }
   }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort with alternate comparer:

Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Oviraptor":

Oviraptor
Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaur":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "":


Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus
 */