# 54.二叉搜索树的第k大节点

### 一、 题目

给定一棵二叉搜索树，请找出其中第 k 大的节点的值。

示例 1:

输入: root = \[3,1,4,null,2], k = 1

```
3
/ \
1   4
\
   2
```

输出: 4

示例 2:

输入: root = \[5,3,6,2,4,null,null,1], k = 3

```
 5
/ \
3   6
/ \
2   4
/
1
```

输出: 4   限制：

1 ≤ k ≤ 二叉搜索树元素个数

来源：力扣（LeetCode）

链接：<https://leetcode-cn.com/problems/er-cha-sou-suo-shu-de-di-kda-jie-dian-lcof>

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

### 二、 分析

根据二叉搜索树的特性，我们通过中序遍历得到有序的数组就可以轻松获得结果

```
func kthLargest(_ root: TreeNode?, _ k: Int) -> Int {
    var inorderArr: [Int] = []
    
    func inorder(_ node: TreeNode?) {
        guard let n = node else {
            return
        }
        
        inorder(n.right)
        inorderArr.append(n.val)
        inorder(n.left)
    }
    
    inorder(root)
    
    return inorderArr[k - 1]
}
```


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