270

class Solution:
    def closestValue(self, root: TreeNode, target: float) -> int:

        best = float('inf')

        while root:
            if abs(target - root.val) < abs(target - best):
                best = root.val
            if root.val > target:
                root = root.left
            elif root.val < target:
                root = root.right
            else:
                break

        return best