Python Binary Search Tree: Delete a node in a given Binary search tree (BST)

Last update on April 23 2025 12:49:51 (UTC/GMT +8 hours)

4. Delete Node in BST

Write a Python program to delete a node with the given key in a given binary search tree (BST).

Note: Search for a node to remove. If the node is found, delete the node.

Sample Solution:

Python Code:

# Definition: Binary tree node.
class TreeNode(object):
    def __init__(self, x):
         self.val = x
         self.left = None
         self.right = None

def delete_Node(root, key):
  # if root doesn't exist, just return it
	if not root: 
		return root
	# Find the node in the left subtree	if key value is less than root value
	if root.val > key: 
		root.left = delete_Node(root.left, key)
	# Find the node in right subtree if key value is greater than root value, 
	elif root.val < key: 
		root.right= delete_Node(root.right, key)
	# Delete the node if root.value == key
	else: 
	# If there is no right children delete the node and new root would be root.left
		if not root.right:
			return root.left
	# If there is no left children delete the node and new root would be root.right	
		if not root.left:
			return root.right
  # If both left and right children exist in the node replace its value with 
  # the minmimum value in the right subtree. Now delete that minimum node
  # in the right subtree
		temp_val = root.right
		mini_val = temp_val.val
		while temp_val.left:
			temp_val = temp_val.left
			mini_val = temp_val.val
  # Delete the minimum node in right subtree
		root.right = deleteNode(root.right,root.val)
	return root

def preOrder(node): 
    if not node: 
        return      
    print(node.val)
    preOrder(node.left) 
    preOrder(node.right)   
    
root = TreeNode(5)  
root.left = TreeNode(3)  
root.right = TreeNode(6) 
root.left.left = TreeNode(2)  
root.left.right = TreeNode(4) 
root.left.right.left = TreeNode(7)  
print("Original node:")
print(preOrder(root))
result = delete_Node(root, 4)
print("After deleting specified node:")
print(preOrder(result))

Sample Output:

Original node:
5
3
2
4
7
6
None
After deleting specified node:
5
3
2
7
6
None

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to delete a node with a given key from a BST and then perform an in-order traversal to verify the tree remains valid.
Write a Python script to remove a node from a BST, handling all three cases (leaf, one child, two children), and then print the tree level-by-level.
Write a Python program to implement node deletion in a BST and then measure the tree’s height before and after deletion to observe the impact on balance.
Write a Python function to delete a node from a BST and then output both the deleted node’s value and the updated tree structure.

Go to:

Previous: Write a Python program to check whether a given a binary tree is a valid binary search tree (BST) or not.
Next: Write a Python program to convert a given array elements to a height balanced Binary Search Tree (BST).

Python Code Editor:

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