Validate Binary Search Tree

main.py

class Solution:
    def isValidBST(self, node, mini=-inf, maxi=inf):
        if not node:
            return True
        if not mini < node.val < maxi:
            return False
        left_is_valid, right_is_valid = True, True
        if node.left:
            if node.left.val >= node.val:
                left_is_valid = False
            else:
                left_is_valid = self.isValidBST(node.left, mini, min(maxi, node.val))
        if node.right:
            if node.right.val <= node.val:
                right_is_valid = False
            else:
                right_is_valid = self.isValidBST(node.right, max(mini, node.val), maxi)
        return left_is_valid and right_is_valid