Help me understand Inorder Traversal without using recursion

Question

I am able to understand preorder traversal without using recursion, but I\'m having a hard time with inorder traversal. I just don\'t seem to get it, perhaps, because I have

Answer 1

Here is a sample of in order traversal using stack in c# (.net):

(for post order iterative you may refer to: Post order traversal of binary tree without recursion)

public string InOrderIterative()
        {
            List nodes = new List();
            if (null != this._root)
            {
                Stack stack = new Stack();
                var iterativeNode = this._root;
                while(iterativeNode != null)
                {
                    stack.Push(iterativeNode);
                    iterativeNode = iterativeNode.Left;
                }
                while(stack.Count > 0)
                {
                    iterativeNode = stack.Pop();
                    nodes.Add(iterativeNode.Element);
                    if(iterativeNode.Right != null)
                    {
                        stack.Push(iterativeNode.Right);
                        iterativeNode = iterativeNode.Right.Left;
                        while(iterativeNode != null)
                        {
                            stack.Push(iterativeNode);
                            iterativeNode = iterativeNode.Left;
                        }
                    }
                }
            }
            return this.ListToString(nodes);
        }

Here is a sample with visited flag:

public string InorderIterative_VisitedFlag()
        {
            List nodes = new List();
            if (null != this._root)
            {
                Stack stack = new Stack();
                BinaryTreeNode iterativeNode = null;
                stack.Push(this._root);
                while(stack.Count > 0)
                {
                    iterativeNode = stack.Pop();
                    if(iterativeNode.visted)
                    {
                        iterativeNode.visted = false;
                        nodes.Add(iterativeNode.Element);
                    }
                    else
                    {
                        iterativeNode.visted = true;
                        if(iterativeNode.Right != null)
                        {
                            stack.Push(iterativeNode.Right);
                        }
                        stack.Push(iterativeNode);
                        if (iterativeNode.Left != null)
                        {
                            stack.Push(iterativeNode.Left);
                        }
                    }
                }
            }
            return this.ListToString(nodes);
        }

the definitions of the binarytreenode, listtostring utility:

string ListToString(List list)
        {
            string s = string.Join(", ", list);
            return s;
        }


class BinaryTreeNode
    {
        public int Element;
        public BinaryTreeNode Left;
        public BinaryTreeNode Right;        
    }