[Swift]LeetCode270. 最近的二分搜索树的值 $ Closest Binary Search Tree Value

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址： https://www.cnblogs.com/strengthen/p/10648080.html 
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

---

给定一个非空的二进制搜索树和一个目标值，在BST中查找最接近目标的值。 

注： 

• 给定的目标值是一个浮点。
• 您保证在BST中只有一个最接近目标的唯一值。

---

 Solution:

public class TreeNode {
    public var val: Int
    public var left: TreeNode?
    public var right: TreeNode?
    public init(_ val: Int) {
        self.val = val
        self.left = nil
        self.right = nil
    }
}

class Solution {
    func closestValue(_ root: TreeNode?,_ target:Double) -> Int {
        var a:Int = root!.val
        var t:TreeNode? = target < Double(a) ? root?.left : root?.right
        if t == nil {return a}
        var b:Int = closestValue(t, target)
        return abs(Double(a) - target) < abs(Double(b) - target) ? a : b
    }
}