Python Binary Search Tree: Check a binary tree is valid or not
Python Binary Search Tree: Exercise-3 with Solution
Write a Python program to check whether a given a binary tree is a valid binary search tree (BST) or not.
Let a binary search tree (BST) is defined as follows:
The left subtree of a node contains only nodes with keys less than the node's key.
The right subtree of a node contains only nodes with keys greater than the node's key.
Both the left and right subtrees must also be binary search trees.
Example 1: 2 / \ 1 3 Binary tree [2,1,3], return true. Example 2: 1 / \ 2 3 Binary tree [1,2,3], return false.
Sample Solution:
Python Code:
class TreeNode(object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None
def is_BST(root):
stack = []
prev = None
while root or stack:
while root:
stack.append(root)
root = root.left
root = stack.pop()
if prev and root.val <= prev.val:
return False
prev = root
root = root.right
return True
root = TreeNode(2)
root.left = TreeNode(1)
root.right = TreeNode(3)
result = is_BST(root)
print(result)
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
result = is_BST(root)
print(result)
Sample Output:
True False
Flowchart:
Python Code Editor:
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Previous: Write a Python program to find the closest value of a given target value in a given non-empty Binary Search Tree (BST) of unique values.
Next: Write a Python program to delete a node with the given key in a given Binary search tree (BST).
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Python: Tips of the Day
Find current directory and file's directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
import os cwd = os.getcwd()
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
- os.path.dirname(path) (returns "the directory name of pathname path")
- os.getcwd() (returns "a string representing the current working directory")
- os.chdir(path) ("change the current working directory to path")
Ref: https://bit.ly/3fy0R6m
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