在二进制搜索树中查找最接近的值- Python

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def closestValue(root, target):
    if not root:
        return None
    if root.val == target:
        return root.val
    if target < root.val:
        if not root.left:
            return root.val
        left_closest = closestValue(root.left, target)
        return root.val if abs(root.val - target) < abs(left_closest - target) else left_closest
    else:
        if not root.right:
            return root.val
        right_closest = closestValue(root.right, target)
        return root.val if abs(root.val - target) < abs(right_closest - target) else right_closest

def closestValue(root, target):
    closest = root.val
    while root:
        closest = min(root.val, closest, key=lambda x: abs(target - x))
        root = root.left if target < root.val else root.right
    return closest