Validating a Binary Search Tree (BST): Depth-First Search & Range Bounds Analysis

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def is_valid_bst(root: TreeNode) -> bool:
    def validate(node, low=float('-inf'), high=float('inf')):
        if not node:
            return True
        if not (low < node.val < high):
            return False
        return validate(node.left, low, node.val) and validate(node.right, node.val, high)
    return validate(root)

root = TreeNode(10, TreeNode(5), TreeNode(15))
print("Is Valid BST:", is_valid_bst(root))