Delete a node from BST Python

PROGRAM TO DELETE A NODE IN BINARY SEARCH TREE




class Node:

 

    # Constructor to create a new node

    def __init__(self, key):

        self.key = key

        self.left = None

        self.right = None

 

 

# A utility function to do inorder traversal of BST

def inorder(root):

    if root is not None:

        inorder(root.left)

        print root.key,

        inorder(root.right)

 

 

# A utility function to insert a

# new node with given key in BST

def insert(node, key):

 

    # If the tree is empty, return a new node

    if node is None:

        return Node(key)

 

    # Otherwise recur down the tree

    if key < node.key:

        node.left = insert(node.left, key)

    else:

        node.right = insert(node.right, key)

 

    # return the (unchanged) node pointer

    return node

 

# Given a non-empty binary

# search tree, return the node

# with minum key value

# found in that tree. Note that the

# entire tree does not need to be searched

 

 

def minValueNode(node):

    current = node

 

    # loop down to find the leftmost leaf

    while(current.left is not None):

        current = current.left

 

    return current

 

# Given a binary search tree and a key, this function

# delete the key and returns the new root

 

 

def deleteNode(root, key):

 

    # Base Case

    if root is None:

        return root

 

    # If the key to be deleted

    # is smaller than the root's

    # key then it lies in  left subtree

    if key < root.key:

        root.left = deleteNode(root.left, key)

 

    # If the kye to be delete

    # is greater than the root's key

    # then it lies in right subtree

    elif(key > root.key):

        root.right = deleteNode(root.right, key)

 

    # If key is same as root's key, then this is the node

    # to be deleted

    else:

 

        # Node with only one child or no child

        if root.left is None:

            temp = root.right

            root = None

            return temp

 

        elif root.right is None:

            temp = root.left

            root = None

            return temp

 

        # Node with two children:

        # Get the inorder successor

        # (smallest in the right subtree)

        temp = minValueNode(root.right)

 

        # Copy the inorder successor's

        # content to this node

        root.key = temp.key

 

        # Delete the inorder successor

        root.right = deleteNode(root.right, temp.key)

 

    return root

 

 

# Driver code

""" Let us create following BST

              50

           /     \

          30      70

         /  \    /  \

       20   40  60   80 """

 

root = None

root = insert(root, 50)

root = insert(root, 30)

root = insert(root, 20)

root = insert(root, 40)

root = insert(root, 70)

root = insert(root, 60)

root = insert(root, 80)

 

print "Inorder traversal of the given tree"

inorder(root)

 

print "\nDelete 20"

root = deleteNode(root, 20)

print "Inorder traversal of the modified tree"

inorder(root)

 

print "\nDelete 30"

root = deleteNode(root, 30)

print "Inorder traversal of the modified tree"

inorder(root)

 

print "\nDelete 50"

root = deleteNode(root, 50)

print "Inorder traversal of the modified tree"

inorder(root)




OUTPUT:

Inorder traversal of the given tree
20 30 40 50 60 70 80
Delete 20
Inorder traversal of the modified tree
30 40 50 60 70 80
Delete 30
Inorder traversal of the modified tree
40 50 60 70 80
Delete 50
Inorder traversal of the modified tree
40 60 70 80

CREDITS: https://www.geeksforgeeks.org/binary-search-tree-set-2-delete/