TreeTraversalIterative.cs

public class TreeNode<T> where T : IComparable<T>
{
  public T Value { get; set; }
  public TreeNode<T> Left { get; set; }
  public TreeNode<T> Right { get; set; }
  public TreeNode<T> Parent { get; set; }
}

public static class TreeTraversalIterative
{
  public static void PreOrderTraversal<T>(TreeNode<T> root, Action<T> action) where T : IComparable<T>
  {
    if(root == null)
      return;
    
    var stack = new System.Collections.Generic.Stack<TreeNode<T>>();
    var curr = root;
    
    while(true) {
      if(curr != null) {
        action(curr.Value);
        stack.Push(curr.Right);
        curr = curr.Left;
      } else {
        if(stack.Count == 0) {
          break;
        } else {
          curr = stack.Pop();
        }
      }//end-if-else
    }//end-while
  }
  
  
  public static void InOrderTraversal<T>(TreeNode<T> root, Action<T> action) where T : IComparable<T>
  {
    if(root == null)
      return;
    
    var stack = new System.Collections.Generic.Stack<TreeNode<T>>();
    var curr = root;
    
    while(true) {
      if(curr != null) {
        stack.Push(curr);
        curr = curr.Left;
      } else {
        if(stack.Count == 0) {
          break;
        } else {
          curr = stack.Pop();
          action(curr.Value);
          curr = curr.Right;
        }
      }//end-if-else
    }//end-while
  }
  
  
  public static void PostOrderTraversal<T>(TreeNode<T> root, Action<T> action) where T : IComparable<T>
  {
    if(root == null)
      return;
    
    TreeNode<T> prev = null;
    var stack = new System.Collections.Generic.Stack<TreeNode<T>>();
    
    stack.Push(root);
    
    while(stack.Count > 0) {
      var curr = stack.Peek();
    
      if(prev == null || prev.Left == curr || prev.Right == curr) {
        if(curr.Left != null) {
          stack.Push(curr.Left);
        } else if(curr.Right != null) {
          stack.Push(curr.Right);
        }
      } else if (prev == curr.Left) {
        if(curr.Right != null) 
          stack.Push(curr.Right);
      } else {
        action(curr.Value);
        stack.Pop();
      }
      
      prev = curr;
    }//end-while
  }
  
}