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Given a binary tree root and an integer target, delete all the leaf nodes with value target.

Note that once you delete a leaf node with value target, if it's parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you can't).

Example 1:

Input: root = [1,2,3,2,null,2,4], target = 2
Output: [1,null,3,null,4]
Explanation: Leaf nodes in green with value (target = 2) are removed (Picture in left). 
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).
Example 2:

Input: root = [1,3,3,3,2], target = 3
Output: [1,3,null,null,2]
Example 3:

Input: root = [1,2,null,2,null,2], target = 2
Output: [1]
Explanation: Leaf nodes in green with value (target = 2) are removed at each step.
Example 4:

Input: root = [1,1,1], target = 1
Output: []
Example 5:

Input: root = [1,2,3], target = 1
Output: [1,2,3]
 

Constraints:

1 <= target <= 1000
Each tree has at most 3000 nodes.
Each node's value is between [1, 1000].

给你一棵以 root 为根的二叉树和一个整数 target ，请你删除所有值为 target 的 叶子节点 。

注意，一旦删除值为 target 的叶子节点，它的父节点就可能变成叶子节点；如果新叶子节点的值恰好也是 target ，那么这个节点也应该被删除。

也就是说，你需要重复此过程直到不能继续删除。

示例 1：

输入：root = [1,2,3,2,null,2,4], target = 2
输出：[1,null,3,null,4]
解释：
上面左边的图中，绿色节点为叶子节点，且它们的值与 target 相同（同为 2 ），它们会被删除，得到中间的图。
有一个新的节点变成了叶子节点且它的值与 target 相同，所以将再次进行删除，从而得到最右边的图。
示例 2：

输入：root = [1,3,3,3,2], target = 3
输出：[1,3,null,null,2]
示例 3：

输入：root = [1,2,null,2,null,2], target = 2
输出：[1]
解释：每一步都删除一个绿色的叶子节点（值为 2）。
示例 4：

输入：root = [1,1,1], target = 1
输出：[]
示例 5：

输入：root = [1,2,3], target = 1
输出：[1,2,3]
 

提示：

1 <= target <= 1000
每一棵树最多有 3000 个节点。
每一个节点值的范围是 [1, 1000] 。

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     public var val: Int
 5  *     public var left: TreeNode?
 6  *     public var right: TreeNode?
 7  *     public init(_ val: Int) {
 8  *         self.val = val
 9  *         self.left = nil
10  *         self.right = nil
11  *     }
12  * }
13  */
14 class Solution {
15     func removeLeafNodes(_ root: TreeNode?, _ target: Int) -> TreeNode? {
16         if root == nil {return nil}
17         let left:TreeNode? = removeLeafNodes(root?.left, target)
18         let right:TreeNode? = removeLeafNodes(root?.right, target)
19         if left == nil && right == nil && root?.val == target
20         {
21             return nil
22         }
23         root?.left=left
24         root?.right=right
25         return root
26     }
27 }