VB2003下实现的KMP查找算法

增强型的模式匹配算法，KMP查找算法。全称是克努特-莫里斯-普拉特算法。是一种在一个串内查找第一个匹配子串位置的算法。之所以是增强型的，是应为它修改普通算法中失配的时候，被查找串的查找起始位置只向后移动一个单位的办法。通过首先分析匹配串的逻辑，给每一个项目位置加入一个权值。这样在失配的时候，就可以根据失配项目单位所对应的权值，顺移多个位置再次匹配。具体的算法可以参考《数据结构》一书。

现在我用VB.NET 2003实现这个算法。主函数KMPSearch进行实际的匹配操作。子函数KMPSearchGetNextArray负责计算匹配串每个项目单位对应的权值。

稍后推出使用VB2005泛型的KMP查找算法。

        Public Shared Function KMPSearch(ByVal src As Array, ByVal key As Array) As Integer

            Dim ret As Integer = 0

            Dim arrNext() As Integer

            Dim inti As Integer = 1

            Dim intj As Integer = 1

            If src Is Nothing OrElse key Is Nothing OrElse key.Length > src.Length Then

                ret = -1

            Else

                arrNext = KMPSearchGetNextArray(key)

                While inti <= src.Length AndAlso intj <= key.Length

                    If intj = 0 OrElse (Equals(src(inti - 1), key(intj - 1)) = True) Then

                        inti = inti + 1

                        intj = intj + 1

                    Else

                        intj = arrNext(intj)

                    End If

                End While

                If intj > key.Length Then

                    ret = inti - key.Length - 1

                Else

                    ret = -1

                End If

            End If

            Return ret

        End Function

 

        Private Shared Function KMPSearchGetNextArray(ByVal key As Array) As Integer()

            Dim arrNext(key.Length) As Integer

            Dim intj As Integer = 1

            Dim intk As Integer = 0

            arrNext(1) = 0

            While intj < key.Length

                If intk = 0 OrElse (Equals(key(intj - 1), key(intk - 1)) = True) Then

                    intj = intj + 1

                    intk = intk + 1

                    arrNext(intj) = intk

                Else

                    intk = arrNext(intk)

                End If

            End While

            Return arrNext

        End Function