Posted on Jun 29, 2021 • Edited on Jul 8, 2021

deletion in binary search tree

#algorithms #beginners #codenewbie #computerscience

hi, this is part 5 of tree data structure, and the #day_17 of algorithms and data structure, In the last posts, we talked about the binary search tree, its advantages, disadvantages, time and space complexity of its basic operations such as searching, insertion, and also their implementation using python
In this post, we'll discuss deletion :)

last posts:
+ insertion, searching in binary search tree
+ introduction to binary search tree

Deletion in the binary search tree

there are 3 cases in deletion in binary search tree (reference):

if the node to be deleted is the leaf, this is the easiest case, we will only remove it without moving anything :)
if the node to be deleted has one child, in this case, we will replace the child with the node and delete the child
if the node to be deleted has two children, in this case, we need to find a successor (the min of right sub-tree) or a predecessor (the max of left sub-tree), and copy it to the node to be deleted, then delete the successor (or the predecessor)

Deletion implementation

before the implementation of deletion, we need to create a function that returns to us a successor.

getSuccessor function

def getSuccessor(currentNode): while currentNode.left: currentNode = currentNode.left return currentNode

Delete function

more details...

def delete(value: int, root): """ [code is from] => https://www.geeksforgeeks.org/binary-search-tree-set-2-delete/ """ # if the tree is empty  if root is None: return root # if value is smaller than the root's value  if value < root.value: root.left = delete(value , root.left) # if value is greater than the root's value  elif(value > root.value): root.right = delete(value, root.right) else: #! case1 or case2 (node has not children or has only one)  if root.left is None: temp = root.right root = None return temp elif root.right is None: temp = root.left root = None return temp #! case: node has 2 children  # getting successor  temp = getSuccessor(root.right) # Copy the successor's value to the node's value  root.value = temp.value # Delete the successor  root.right = delete(temp.value, root.right) return root