Python Binary Search Tree: Find the k^th smallest element in a given a binary search tree (BST)

Last update on April 23 2025 12:49:50 (UTC/GMT +8 hours)

6. Kth Smallest in BST

Write a Python program to find the k^th smallest element in a given binary search tree.

Sample Solution:

Python Code:

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

def kth_smallest(root, k):
    stack = []
    while root or stack:
        while root:
            stack.append(root)
            root = root.left
        root = stack.pop()
        k -= 1
        if k == 0:
            break
        root = root.right
    return root.val

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)  

print(kth_smallest(root, 2))
print(kth_smallest(root, 3))

Sample Output:

5
8

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to find the kth smallest element in a BST using in-order traversal and then return the element along with its rank.
• Write a Python script to implement a recursive function that returns the kth smallest element in a BST, handling edge cases where k is out of bounds.
• Write a Python program to compute the kth smallest element in a BST and then compare the result with a sorted array conversion of the tree’s elements.
• Write a Python function to determine the kth smallest element in a BST and print the path from the root to that element.

Go to:

• Python Binary Search Tree Exercises Home ↩
• Python Exercises Home ↩

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