从 DataTable 结构计算前序树遍历

Question

我有一个具有以下结构的 DataTable：

Root | Level 1 | Level 2 | Level 3 | Tree L | Tree R
Food                                 1        18
       Fruit                         2        11
                 Red                 3        6
                           Cherry    4        5
                 Yellow              7        10
                           Banana    8        9
       Meat                          12       17
                 Beef                13       14
                 Pork                15       16

使用 C#，我需要遍历这个结构并为每个节点计算正确的 Tree L 和 Tree R 值。这只是一个例子，真正的结构有数百个节点，至少达到 7 级，但可能更多。

谁能建议我如何处理计算左右值的代码？

Answer 1

因此，您想要跟踪树的访问顺序，但您将顺序拆分为 L 和 R。这些对应于Node 结构的Visit 函数的“入口”和“出口”。假设 Node 类具有 Node.Visit() 方法，您可以：

private static List<Tuple<char,Node>> VisitOrder = new List<Tuple<char,Node>>();

public void Visit()
{
    VisitOrder.Add(Tuple.Create('L', this));
    // whatever visit logic you use here
    VisitOrder.Add(Tuple.Create('R', this));
}

完成后，您所要做的就是查看VisitOrder 值。它们以升序存储在List 中，其中索引对应于它在访问序列中的位置。那么List 中的每个项目都是一个Tuple，描述它对应于哪个值以及它访问了哪个Node。

编辑：

要获得最终的输出格式，您可以执行以下操作：

var LTree = VisitOrder
    .Where(t => t.First == 'L')
    .Select((t, i) => String.Format("{0}) {1}", i + 1, t.Second.Name));
var RTree = VisitOrder
    .Where(t => t.First == 'R')
    .Select((t, i) => String.Format("{0}) {1}", i + 1, t.Second.Name));

Answer 2

我是这样理解的：

private class FolderRow
    {
        public int Indent
        {
            get { return this.Row.GetValue("Indent", 0); }
            set { this.Row["Indent"] = value; }
        }
        public int Left
        {
            get { return this.Row.GetValue("Tree L", 0); }
            set { this.Row["Tree L"] = value; }
        }
        public int Right
        {
            get { return this.Row.GetValue("Tree R", 0); }
            set { this.Row["Tree R"] = value; }
        }
        public Guid Id
        {
            get { return this.Row.GetValue("FolderID", Guid.Empty); }

        }
        public DataRow Row { get; private set; }

        public int RowNum { get; set; }

        public bool RowComplete { get { return this.Left > 0 && this.Right > 0; } }

        public FolderRow(DataRow row, int rowNum)
        {
            this.Row = row;
            this.RowNum = rowNum;
        }
    }    

[TestMethod]
public void ImportFolderStructure()
{
    var inputTable = FileUtil.GetDataSetFromExcelFile(new FileInfo(@"c:\SampleTree.xlsx")).Tables[0];

    var currentLevel = 0;
    var nodeCount = 1;
    var currentRow = 0;

    inputTable.Columns.Add("Indent", typeof (int));
    inputTable.Columns.Add("Path", typeof (string));

    var rightStack = new List<FolderRow>();

    foreach (DataRow row in inputTable.Rows)
        row["Indent"] = GetLevelPopulated(row);

    foreach (DataRow row in inputTable.Rows)
    {
        if (row.GetValue("Indent", 0) == 0)
            row["Tree L"] = 1;                

    }

    while (true)
    {
        var row = GetRow(inputTable, currentRow);
        if (row.Indent == 0)
        {
            currentRow++;
            rightStack.Add(row);
            continue; 
        }

        // if the indent of this row is greater than the previous row ...
        if (row.Indent > currentLevel)
        {
            currentLevel++;
            nodeCount++;
            row.Left = nodeCount;
            // ... check the next row to see if it is further indented
            currentRow = HandleNextRow(row, currentRow, rightStack, inputTable, ref currentLevel, ref nodeCount);
        } else if (row.Indent == currentLevel)
        {
            nodeCount++;
            row.Left = nodeCount;
            currentRow = HandleNextRow(row, currentRow, rightStack, inputTable, ref currentLevel, ref nodeCount);
        } else if (row.Indent < currentLevel)
        {
            currentLevel--;
            nodeCount++;
            row.Left = nodeCount;
            currentRow = HandleNextRow(row, currentRow, rightStack, inputTable, ref currentLevel, ref nodeCount);
        }

        if (inputTable.Rows.Cast<DataRow>().Select(r => new FolderRow(r, -1)).All(r => r.RowComplete))
            break;

    }

}

private int HandleNextRow(FolderRow row, int currentRow, List<FolderRow> rightStack, DataTable inputTable, ref int currentLevel,
                          ref int nodeCount)
{
    var nextRow = GetRow(inputTable, currentRow + 1);
    if (nextRow != null)
    {
        if (nextRow.Indent > row.Indent)
        {
            // ok the current row has a child so we will need to set the tree right of that, add to stack
            rightStack.Add(row);
        }
        else if (nextRow.Indent == row.Indent)
        {
            nodeCount++;
            row.Right = nodeCount;
        }
        else if (nextRow.Indent < row.Indent)
        {
            nodeCount++;
            row.Right = nodeCount;
            nodeCount++;
            // here we need to get the most recently added row to rightStack, set the Right to the current nodeCount
            var stackLast = rightStack.LastOrDefault();
            if (stackLast != null)
            {
                stackLast.Right = nodeCount;
                rightStack.Remove(stackLast);
            }

            currentLevel--;
        }

        currentRow++;

        if (rightStack.Count > 1)
        {
            // before we move on to the next row, we need to check if there is more than one row still in right stack and 
            // the new current row's ident is less than the current branch (not current leaf)
            var newCurrentRow = GetRow(inputTable, currentRow);
            var stackLast = rightStack.LastOrDefault();
            if (newCurrentRow.Indent == stackLast.Indent)
            {
                nodeCount++;
                stackLast.Right = nodeCount;
                rightStack.Remove(stackLast);

            }
        }


    }
    else
    {
        // reached the bottom
        nodeCount++;
        row.Right = nodeCount;

        // loop through the remaining items in rightStack and set their right values
        var stackLast = rightStack.LastOrDefault();
        while (stackLast != null)
        {
            nodeCount++;
            stackLast.Right = nodeCount;
            rightStack.Remove(stackLast);
            stackLast = rightStack.LastOrDefault();
        }
    }
    return currentRow;
}

private FolderRow GetRow(DataTable inputTable, int rowCount)
{
    if (rowCount >= inputTable.Rows.Count)
        return null;

    return rowCount < 0 ? null : new FolderRow(inputTable.Rows[rowCount],rowCount);
}

private int GetLevelPopulated(DataRow row)
{
    var level = 0;

    while (level < 14)
    {
        if (level == 0 && row["Root"] != DBNull.Value)
            return level;

        level++;

        if (row["Level " + level] != DBNull.Value)
            return level;
    }

    return -1;
}