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

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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.

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給定一個非空的二進制搜索樹和一個目標值，在BST中查找最接近目標的值。 

注： 

• 給定的目標值是一個浮點。
• 您保證在BST中只有一個最接近目標的惟一值。

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 Solution:

 1 public class TreeNode {
 2     public var val: Int
 3     public var left: TreeNode?
 4     public var right: TreeNode?
 5     public init(_ val: Int) {
 6         self.val = val
 7         self.left = nil
 8         self.right = nil
 9     }
10 }
11 
12 class Solution {
13     func closestValue(_ root: TreeNode?,_ target:Double) -> Int {
14         var a:Int = root!.val
15         var t:TreeNode? = target < Double(a) ? root?.left : root?.right
16         if t == nil {return a}
17         var b:Int = closestValue(t, target)
18         return abs(Double(a) - target) < abs(Double(b) - target) ? a : b
19     }
20 }