Insertion in binary search tree using recursion in python

Python program for Insertion in binary search tree using recursion. Here problem description and explanation.

#  Python 3 program for
#  Insertion in binary search tree by using recursion
class TreeNode :
	def __init__(self, data) :
		self.data = data
		self.left = None
		self.right = None
	

class BinarySearchTree :
	def __init__(self) :
		self.root = None
	
	#  Insert a node element
	def addNode(self, node, data) :
		if (node != None) :
			if (node.data >= data) :
				#  When new element is smaller or
				#  equal to current node
				node.left = self.addNode(node.left, data)
			else :
				#  When new element is higher to current node
				node.right = self.addNode(node.right, data)
			
			#  important to manage root node
			return node
		else :
			return TreeNode(data)
		
	
	#  Display preorder
	def preorder(self, node) :
		if (node != None) :
			#  Display node value
			print(" ", node.data, end = "")
			#  Visit to left subtree
			self.preorder(node.left)
			#  Visit to right subtree
			self.preorder(node.right)
		
	
	def inorder(self, node) :
		if (node != None) :
			#  Visit to left subtree
			self.inorder(node.left)
			#  Display node value
			print(" ", node.data, end = "")
			#  Visit to right subtree
			self.inorder(node.right)
		
	
	def postorder(self, node) :
		if (node != None) :
			#  Visit to left subtree
			self.postorder(node.left)
			#  Visit to right subtree
			self.postorder(node.right)
			#  Display node value
			print(" ", node.data, end = "")
		
	

def main() :
	tree = BinarySearchTree()
	#         10
	#        / \
	#       /   \
	#      4     15
	#     / \   /
	#    3   5 12
	#    -------------
	#    Build binary search tree
	tree.root = tree.addNode(tree.root, 10)
	tree.addNode(tree.root, 4)
	tree.addNode(tree.root, 3)
	tree.addNode(tree.root, 5)
	tree.addNode(tree.root, 15)
	tree.addNode(tree.root, 12)
	#  Display tree nodes
	print("Preorder ")
	tree.preorder(tree.root)
	print("\nInorder ")
	tree.inorder(tree.root)
	print("\nPostorder ")
	tree.postorder(tree.root)

if __name__ == "__main__": main()

Output

Preorder
  10  4  3  5  15  12
Inorder
  3  4  5  10  12  15
Postorder
  3  5  4  12  15  10


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