The naive idea is to use the list to save to find the Kth in

reverse order traversal, but it is too troublesome . Recursive thinking is to traverse to the Kth order when traversing in reverse order and return directly to the Kth.

```
int res = 0;
int k;
public int kthLargest(TreeNode root, int k) {
this.k = k;
disIn(root);
return res;
}
void disIn(TreeNode root){
//反中序遍历
if (k < 1 || root == null) return ;//已经找到第K个
kthLargest(root.right,k);//找到最右侧
if (k == 1){
//第K大
res = root.val;
}
k--;//遍历的元素个数
kthLargest(root.left,k);
}
```