Breadth-first traversal

Question

I was trying to solve one interview question, but for that I have to travel the binary tree level by level. I have designed BinaryNode with having below variable

Answer 1

using DFS approach: The tree traversal is O(n)

public class NodeLevel
{
    public TreeNode Node { get; set;}
    public int Level { get; set;}
}

public class NodeLevelList
{
    private Dictionary> finalLists = new Dictionary>();

    public void AddToDictionary(NodeLevel ndlvl)
    {
        if(finalLists.ContainsKey(ndlvl.Level))
        {
            finalLists[ndlvl.Level].Add(ndlvl.Node);
        }
        else
        {
            finalLists.Add(ndlvl.Level,new List(){ndlvl.Node});
        }
    }

    public Dictionary> GetFinalList()
    {
        return finalLists;
    }
}

The method that does traversal:

public static void DFSLevel(TreeNode root, int level, NodeLevelList nodeLevelList)
{
    if(root == null)
        return;

    nodeLevelList.AddToDictionary(new NodeLevel{Node = root, Level = level});

    level++;

    DFSLevel(root.Left,level,nodeLevelList);
    DFSLevel(root.Right,level,nodeLevelList);

}