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CheckValidityBST Solution uploaded!

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	`1`	`+`
	`2`	`+`
	`3`	`+# Definition for a binary tree node.`
	`4`	`+# class TreeNode:`
	`5`	`+# def __init__(self, val=0, left=None, right=None):`
	`6`	`+# self.val = val`
	`7`	`+# self.left = left`
	`8`	`+# self.right = right`
	`9`	`+class Solution:`
	`10`	`+ def isValidBST(self, root: Optional[TreeNode]) -> bool:`
	`11`	`+ # Time: O(n)`
	`12`	`+ def valid(node, left, right):`
	`13`	`+ if not node:`
	`14`	`+ return True`
	`15`	`+ if not (node.val < right and node.val > left):`
	`16`	`+ return False`
	`17`	`+ return (valid(node.left, left, node.val) and`
	`18`	`+ valid(node.right, node.val, right))`
	`19`	`+ return valid(root, float("-inf"), float("inf"))`
	`20`	`+`

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