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BinarySearchTree.py
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# Author: OMKAR PATHAK
# This program illustrates an example of Binary Search Tree using Python
# Binary Search Tree, is a node-based binary tree data structure which has the following properties:
#
# The left subtree of a node contains only nodes with keys less than the node’s key.
# The right subtree of a node contains only nodes with keys greater than the node’s key.
# The left and right subtree each must also be a binary search tree.
# There must be no duplicate nodes.
class Node(object):
def __init__(self, data):
self.data = data
self.leftChild = None
self.rightChild = None
def insert(self, data):
''' For inserting the data in the Tree '''
if self.data == data:
return False # As BST cannot contain duplicate data
elif data < self.data:
''' Data less than the root data is placed to the left of the root '''
if self.leftChild:
return self.leftChild.insert(data)
else:
self.leftChild = Node(data)
return True
else:
''' Data greater than the root data is placed to the right of the root '''
if self.rightChild:
return self.rightChild.insert(data)
else:
self.rightChild = Node(data)
return True
def minValueNode(self, node):
current = node
# loop down to find the leftmost leaf
while(current.leftChild is not None):
current = current.leftChild
return current
def maxValueNode(self, node):
current = node
# loop down to find the leftmost leaf
while(current.rightChild is not None):
current = current.rightChild
return current
def delete(self, data,root):
''' For deleting the node '''
if self is None:
return None
# if current node's data is less than that of root node, then only search in left subtree else right subtree
if data < self.data:
self.leftChild = self.leftChild.delete(data,root)
elif data > self.data:
self.rightChild = self.rightChild.delete(data,root)
else:
# deleting node with one child
if self.leftChild is None:
if self == root:
temp = self.minValueNode(self.rightChild)
self.data = temp.data
self.rightChild = self.rightChild.delete(temp.data,root)
temp = self.rightChild
self = None
return temp
elif self.rightChild is None:
if self == root:
temp = self.maxValueNode(self.leftChild)
self.data = temp.data
self.leftChild = self.leftChild.delete(temp.data,root)
temp = self.leftChild
self = None
return temp
# deleting node with two children
# first get the inorder successor
temp = self.minValueNode(self.rightChild)
self.data = temp.data
self.rightChild = self.rightChild.delete(temp.data,root)
return self
def find(self, data):
''' This function checks whether the specified data is in tree or not '''
if(data == self.data):
return True
elif(data < self.data):
if self.leftChild:
return self.leftChild.find(data)
else:
return False
else:
if self.rightChild:
return self.rightChild.find(data)
else:
return False
def preorder(self):
'''For preorder traversal of the BST '''
if self:
print(str(self.data), end = ' ')
if self.leftChild:
self.leftChild.preorder()
if self.rightChild:
self.rightChild.preorder()
def inorder(self):
''' For Inorder traversal of the BST '''
if self:
if self.leftChild:
self.leftChild.inorder()
print(str(self.data), end = ' ')
if self.rightChild:
self.rightChild.inorder()
def postorder(self):
''' For postorder traversal of the BST '''
if self:
if self.leftChild:
self.leftChild.postorder()
if self.rightChild:
self.rightChild.postorder()
print(str(self.data), end = ' ')
class Tree(object):
def __init__(self):
self.root = None
def insert(self, data):
if self.root:
return self.root.insert(data)
else:
self.root = Node(data)
return True
def delete(self, data):
if self.root is not None:
return self.root.delete(data,self.root)
def find(self, data):
if self.root:
return self.root.find(data)
else:
return False
def preorder(self):
if self.root is not None:
print()
print('Preorder: ')
self.root.preorder()
def inorder(self):
print()
if self.root is not None:
print('Inorder: ')
self.root.inorder()
def postorder(self):
print()
if self.root is not None:
print('Postorder: ')
self.root.postorder()
if __name__ == '__main__':
tree = Tree()
tree.insert(10)
tree.insert(12)
tree.insert(5)
tree.insert(4)
tree.insert(20)
tree.insert(8)
tree.insert(7)
tree.insert(15)
tree.insert(13)
print(tree.find(1))
print(tree.find(12))
''' Following tree is getting created:
10
/ \
5 12
/ \ \
4 8 20
/ /
7 15
/
13
'''
tree.preorder()
tree.inorder()
tree.postorder()
print('\n\nAfter deleting 20')
tree.delete(20)
tree.inorder()
tree.preorder()
print('\n\nAfter deleting 10')
tree.delete(10)
tree.inorder()
tree.preorder()