用 excel VBA 写一个解决车辆最短路径问题的代码

在Excel VBA中编写一个车辆最短路径问题的代码通常涉及到图论中的最短路径算法，如Dijkstra算法或Floyd-Warshall算法。由于Excel本身并不是设计用于处理大规模复杂计算的工具，VBA更适合于小型数据集。以下是一个简单的例子，演示如何用VBA实现Dijkstra算法求解从起始节点到其他节点的最短路径：

Sub DijkstraShortestPath()
    '假设工作表的第一行是节点名，第二列开始存储边的距离
    Dim ws As Worksheet
    Set ws = ThisWorkbook.Worksheets("Sheet1") '<-- 替换为你实际的工作表名称
    
    '定义变量
    Dim nodes() As Variant
    nodes = ws.Range("A2", ws.Cells(ws.Rows.Count, "A").End(xlUp)).Value '获取所有节点
    Dim distance() As Long
    ReDim distance(1 To UBound(nodes), 1 To UBound(nodes))
    For i = 1 To UBound(nodes)
        For j = 1 To UBound(nodes)
            If i <> j Then '避免自环
                distance(i, j) = ws.Cells(i + 1, 2).Value '假设距离在B列
            End If
        Next j
    Next i
    
    '初始化距离数组和已访问数组
    Dim visited() As Boolean
    ReDim visited(1 To UBound(nodes))
    For Each n In nodes
        visited(n) = False
    Next n
    
    'Dijkstra算法核心部分
    Dim startNode As Integer '替换为你起始节点的位置
    Dim current Node As Variant
    Do While Not IsEmpty(current Node)
        '找到未访问且距离最小的节点
        current Node = MinDistance(distance, visited, startNode)
        
        '标记当前节点为已访问并更新相邻节点的最短距离
        visited(current Node) = True
        UpdateAdjacentNodes(distance, current Node, startNode)
    Loop

    '显示结果
    DisplayPaths(nodes, distance)

End Sub

Private Function MinDistance(distance(), visited() As Boolean, startNode As Integer) As Variant
    '查找未访问且距离最小的节点
    Dim minNode As Variant
    Dim minDist As Long
    minDist = &HFFFFFF '较大数值代表无穷大
    For Each node In nodes
        If Not visited(node) And distance(startNode, node) < minDist Then
            minNode = node
            minDist = distance(startNode, node)
        End If
    Next node
    MinDistance = minNode
End Function

Private Sub UpdateAdjacentNodes(distance(), currentNode As Variant, startNode As Integer)
    Dim neighbor As Variant
    For Each neighbor In nodes
        If neighbor <> currentNode Then
            If Not visited(neighbor) Then
                distance(currentNode, neighbor) = distance(startNode, currentNode) + distance(currentNode, neighbor)
            End If
        End If
    Next neighbor
End Sub

Private Sub DisplayPaths(nodes(), distance() As Long)
    '在这里可以遍历distance数组，找出每个节点的最短路径
    '由于Excel不是最适合的地方，你可以选择打印出来，或者将结果导出到另一个工作表
End Sub

注意，这只是一个简化版本，实际应用中可能需要考虑更多的边界条件和优化。同时，对于大型数据集，你可能需要考虑使用专门的网络分析库或者其他更适合的数据结构，而不是仅限于Excel VBA。