#5 most askedVery commonMediumBST
Validate Binary Search Tree
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🏢 Asked in real interviews
No reports yet. Were you asked this? Be the first to say where.Return True if a tree is a valid BST: every node in the left subtree is smaller, and every node in the right subtree is larger, at every level.
[5, 1, 4, None, None, 3, 6] → False (3 is in 5's right subtree).
🧪 Practice
Write your solution, then press Run tests. Explain your approach out loud as you go.
def is_valid_bst(root, low=float("-inf"), high=float("inf")):
pass
Output appears here. Press Run or Ctrl/⌘ + Enter.
Try it first. Struggling for a few minutes is how it sticks.