Python Binary Search Tree: Find the closest value of a target in a given non-empty Binary Search Tree (BST) of unique values

Last update on July 28 2025 12:56:37 (UTC/GMT +8 hours)

2. Closest Value in BST

Write a Python program to find the closest value to a given target value in a given non-empty Binary Search Tree (BST) of unique values.

Sample Solution:

Python Code:

class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def closest_value(root, target):
    a = root.val
    kid = root.left if target < a else root.right
    if not kid:
        return a
    b = closest_value(kid, target)
    return min((a,b), key=lambda x: abs(target-x))

root = TreeNode(8)  
root.left = TreeNode(5)  
root.right = TreeNode(14) 
root.left.left = TreeNode(4)  
root.left.right = TreeNode(6) 
root.left.right.left = TreeNode(8)  
root.left.right.right = TreeNode(7)  
root.right.right = TreeNode(24) 
root.right.right.left = TreeNode(22)  
    
result = closest_value(root, 19)
print(result)

Sample Output:

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to search for the closest value to a target in a BST using an iterative approach and print the closest value found.
Write a Python script to find the closest value to a given target in a BST and also return the difference between the target and the closest value.
Write a Python program to implement a recursive function that navigates a BST and finds the value closest to a specified target, then test it on various target values.
Write a Python function that, given a BST and a target, returns both the closest value and the path taken to reach that value.

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Previous: Write a Python program to create a Balanced Binary Search Tree (BST) using an array (given) elements where array elements are sorted in ascending order.
Next: Write a Python program to check whether a given a binary tree is a valid binary search tree (BST) or not.

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