An elegant, clean python recursive solution.

  • 0

    If anyone has cleaner, simpler solution, plz tell me.

    class Solution(object):
        def isValidBST(self, root):
            def helper(node, lower, upper):  # set boundaries for node.val.
                if (not node):
                    return True
                if lower < node.val < upper:
                    return helper(node.left, lower, node.val) and helper(node.right, node.val, upper)
                    return False
            return helper(root, -2147483649, 2147483648)  # min int and max int will be the bound for root.val

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