Q62: Validate Binary Search Tree. - DSA Patterns (Multi-Lang)

In Simple Words: Pass valid open interval (minVal, maxVal) recursively down the tree. Every node must satisfy minVal < node.val < maxVal. Left child inherits (minVal, node.val); right child inherits (node.val, maxVal).

Time: $O(N)$ | Space: $O(H)$

Multi-Language SolutionsPython 3 • JavaScript • TypeScript • Java • C++

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def isValidBST(root: TreeNode | None) -> bool:
    def validate(node, low, high):
        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, float('-inf'), float('inf'))