Morris Inorder Traversal Python
public class TreeNode
{
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null)
{
this.val = val;
this.left = left;
this.right = right;
}
}
class MorrisTraversal
{
public static IList<int> InOrderTraversal(TreeNode root)
{
IList<int> list = new List<int>();
var current = root;
while (current != null)
{
//When there exist no left subtree
if (current.left == null)
{
list.Add(current.val);
current = current.right;
}
else
{
//Get Inorder Predecessor
//In Order Predecessor is the node which will be printed before
//the current node when the tree is printed in inorder.
//Example:- {1,2,3,4} is inorder of the tree so inorder predecessor of 2 is node having value 1
var inOrderPredecessorNode = GetInorderPredecessor(current);
//If the current Predeccessor right is the current node it means is already printed.
//So we need to break the thread.
if (inOrderPredecessorNode.right != current)
{
inOrderPredecessorNode.right = null;
list.Add(current.val);
current = current.right;
}//Creating thread of the current node with in order predecessor.
else
{
inOrderPredecessorNode.right = current;
current = current.left;
}
}
}
return list;
}
private static TreeNode GetInorderPredecessor(TreeNode current)
{
var inOrderPredecessorNode = current.left;
//Finding Extreme right node of the left subtree
//inOrderPredecessorNode.right != current check is added to detect loop
while (inOrderPredecessorNode.right != null && inOrderPredecessorNode.right != current)
{
inOrderPredecessorNode = inOrderPredecessorNode.right;
}
return inOrderPredecessorNode;
}
}
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