PrePostInorderTraversal

# pre post and inorder traversal
# IN - LEFT, PARENT, RIGHT
# PRE - PARENT, LEFT, RIGHT
# POST - LEFT, RIGHT, PARENT

class node:

  def __init__(self, key):
    
    self.key = key
    self.left = None
    self.right = None

class BST:

  def __init__(self):

    self.root = None
  
  def add(self, key):

    self.root = self._add(key, self.root)
  
  def _add(self, key, current):

    if current is None:
      current = node(key)
    elif key == current.key:
      return
    elif key < current.key:
      current.left = self._add(key, current.left)
    else:
      current.right = self._add(key, current.right)
    
    return current
  
  def inorder(self):
    print('nodes inorder traversal: ')
    self._inorder(self.root)

  def _inorder(self, node):

    if node:
      self._inorder(node.left)
      print(node.key)
      self._inorder(node.right)
  
  def preorder(self):
    print('nodes in preorder traversal: ')
    self._preorder(self.root)

  def _preorder(self, node):

    if node:
      print(node.key)
      self._preorder(node.left)
      self._preorder(node.right)
  
  def postorder(self):
    print('nodes in postorder traversal: ')
    self._postorder(self.root)
  
  def _postorder(self, node):

    if node:
      self._postorder(node.left)
      self._postorder(node.right)
      print(node.key)
      

if __name__ == '__main__':

  a = BST()
  a.add(4)
  a.add(1)
  a.add(6)
  a.add(2)
  a.add(0)
  a.inorder()
  a.preorder()
  a.postorder()