江苏省高校计算机等级考试命题研究院 江苏省高校计算机等级考试辅导
江苏省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、算法说明

1)        顺序查找

         逐个元素找,如果有,则记录位置,然后跳出循环;否则,查找失败。

         代码如下:

                  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,将元素下标保存在index中并结束查找

                                       Index = i

                                       Exit Sub

                              End If

                        Next i

                        Index = -1             '若没找到,则index值为-1

                  End Sub

 

2)        二分法查找

顺序查找效率低下,当数组有序排列时,可以使用二分法查找提高效率。

         算法思想:

代码如下:

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

                        Dim mid As Integer

                        If low > high Then

     '没有查找到

                              index = -1

                              Exit Sub

                        End If

                        mid = (low + high) \ 2 '取查找区间的中点

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

                              index = mid

                              Exit Sub

                        ElseIf Key < a(mid) Then '查找区间在上半部分

                          high = mid - 1

                     Else

                          low = mid + 1    '查找区间在下半部分

                        End If

                        Call birSearch(a, low, high, Key, index) '递归调用查找函数

                  End Sub

调用方法:

                  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、实战练习

         补充代码(2002春二(9))

         C盘根目录下stu.txt文件中以下的格式保存着学生姓名及班号信息。本程序的功能是:读取该文件中的数据,再利用InputvBox输入要查找的学生姓名,通过顺序查找,给出找到或找不到的信息。附图是某同学被找到时显示的信息窗口。

        张文,机械01

        李明,机械01

        王文卉,机械01

       

        何宇宙,电子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("输入欲查找的学生姓名:")

                           Call search(name, stu, k)

                           If k <= n Then

                                    MsgBox 3

                           Else

                                    MsgBox "无此人。"

                           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