計(jì)算機(jī)等級(jí)考試二級(jí)VB常用算法(8)：排序

1、算法說(shuō)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(méi)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(méi)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

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