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江蘇省高校計(jì)算機(jī)等級(jí)考試命題研究院 江蘇省高校計(jì)算機(jī)等級(jí)考試輔導(dǎo)
江蘇省VB常用算法(八)查找- -

VB常用算法(八)查找- -

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Tag查找    算法                                          

1、算法說明

1)        順序查找

         逐個(gè)元素找,如果有,則記錄位置,然后跳出循環(huán);否則,查找失敗。

         代碼如下:

                  Private Sub Search(a(), ByVal Key, Index As Integer)

                        Dim i%

                        For i = LBound(a) To UBound(a)

                              If a(i) = Key Then '找到,將元素下標(biāo)保存在index中并結(jié)束查找

                                       Index = i

                                       Exit Sub

                              End If

                        Next i

                        Index = -1             '若沒找到,則index值為-1

                  End Sub

 

2)        二分法查找

順序查找效率低下,當(dāng)數(shù)組有序排列時(shí),可以使用二分法查找提高效率。

         算法思想:

代碼如下:

                  Private Sub birSearch(a(), ByVal low%, ByVal high%, ByVal Key, index%)

                        Dim mid As Integer

                        If low > high Then

     '沒有查找到

                              index = -1

                              Exit Sub

                        End If

                        mid = (low + high) \ 2 '取查找區(qū)間的中點(diǎn)

                        If Key = a(mid) Then   '查找到,返回下標(biāo)

                              index = mid

                              Exit Sub

                        ElseIf Key < a(mid) Then '查找區(qū)間在上半部分

                          high = mid - 1

                     Else

                          low = mid + 1    '查找區(qū)間在下半部分

                        End If

                        Call birSearch(a, low, high, Key, index) '遞歸調(diào)用查找函數(shù)

                  End Sub

調(diào)用方法:

                  Private Sub Command1_Click()

                        Dim a(11)

                        a(1) = 5: a(2) = 13: a(3) = 19: a(4) = 21: a(5) = 37

                        a(6) = 56: a(7) = 64: a(8) = 75: a(9) = 80: a(10) = 88: a(11) = 92

                        Dim ind As Integer

                        Call birSearch(a, LBound(a), UBound(a), 21, ind)

                        Print ind

                  End Sub

2、實(shí)戰(zhàn)練習(xí)

         補(bǔ)充代碼(2002春二(9))

         C盤根目錄下stu.txt文件中以下的格式保存著學(xué)生姓名及班號(hào)信息。本程序的功能是:讀取該文件中的數(shù)據(jù),再利用InputvBox輸入要查找的學(xué)生姓名,通過順序查找,給出找到或找不到的信息。附圖是某同學(xué)被找到時(shí)顯示的信息窗口。

        張文,機(jī)械01

        李明,機(jī)械01

        王文卉,機(jī)械01

       

        何宇宙,電子02

 

                  Option Explicit

                  Option Base 1

                  Private Sub Form_click()

                           Dim stu() As String, glass() As String, i As Integer

                           Dim n As Integer, name As String, k As Integer

                           Open "c:\stu\stu.txt" For Input As #11

                           Do While 1

                                    2

                                    ReDim Preserve stu(n), glass(n)

                                    Input #11, stu(n), glass(n)

                           Loop

                           name = InputBox("輸入欲查找的學(xué)生姓名:")

                           Call search(name, stu, k)

                           If k <= n Then

                                    MsgBox 3

                           Else

                                    MsgBox "無此人。"

                           End If

                           Close #11

                  End Sub

                  Private Sub search(name As String, stu() As String, k As Integer)

                           Dim i As Integer

                           For i = 1 To UBound(stu)

                                    If name = stu(i) Then

                                             4

                                    End If

                           Next i

                           5

                  End Sub