frmbinarysearch.frm

二分法查找

VERSION 5.00
Begin VB.Form frmBinarySearch 
   Caption         =   "Binary Search"
   ClientHeight    =   3195
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4680
   LinkTopic       =   "Form1"
   ScaleHeight     =   3195
   ScaleWidth      =   4680
   StartUpPosition =   3  '窗口缺省
   Begin VB.CommandButton cmdBinarySearch 
      Caption         =   "BinarySearch"
      Height          =   2685
      Left            =   210
      TabIndex        =   0
      Top             =   210
      Width           =   4185
   End
End
Attribute VB_Name = "frmBinarySearch"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit
Private Sub cmdBinarySearch_Click()
Dim a&(10)
Dim iFoundPosition%
Dim x As Integer
For x = 0 To 9
   a(x) = x
Next x
iFoundPosition = BinarySearch(a, UBound(a), 4)
If iFoundPosition = -1 Then
   MsgBox "Not found!"
Else
   MsgBox "Found " & iFoundPosition
End If
End Sub

'Before using function BinarySearch,you must be sure that the array is sorted in ascending.
Private Function BinarySearch(ByRef ArrayName, ByVal MaxSize As Integer, ByVal SearchValue) As Integer
'ArrayName is array's name.Arguement transfered by array's name which is the address of array's first element
'MaxSize is array's up-bound.Arguement transfered by array's up-bound by function Ubound()
'SearchValue is searched for.Arguement transfered by a constant or a variable which type is variant(Number)
'Function is returned by the position which SearchValue was found.
Dim Low%, High%, Row%
'Low is initialized by array's low-bound.
Low = 0
'High is initialized by array's up-bound.
High = MaxSize
'Loop is starting.
'If Low is fewer than High,exit loop.
Do While Low <= High
   'Get average(Integer) of Low and High into Row variable
   Row = (Low + High) \ 2
   'Decide if SearchValue is found.
   Select Case ArrayName(Row)
      Case SearchValue
         'SearchValue is found,then return the position found to Function,and Exit Function
         BinarySearch = Row + 1
         Exit Function
      Case Is < SearchValue
         'SearchValue isn't found,and hints SearchValue is upside of Row
         'Re-define the Low and High value
         Low = Row + 1
      Case Is > SearchValue
         'SearchValue isn't found,and hints SearchValue is downside of Row
         'Re-define the Low and High value
         High = Row - 1
   End Select
Loop
'Loop is ending.
'If Function isn't exited insite of loop,hints SearchValue isn't in array.
'Return the position not found to Function
BinarySearch = -1
End Function