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.
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)
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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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