二叉搜索树的第k个结点（第k小）

 1 /* function TreeNode(x) {
 2     this.val = x;
 3     this.left = null;
 4     this.right = null;
 5 } */
 6 function KthNode(pRoot, k)
 7 {
 8     // write code here
 9     if(!pRoot || k==0) return null;
10     let arr = [];
11     inOrder(pRoot, arr, k)
12     return arr[k-1];
13 }
14 function inOrder(root, arr, k){
15     if(root.left) inOrder(root.left, arr, k)
16     if(arr.length == k) return;
17     else arr.push(root);
18     if(root.right) inOrder(root.right, arr, k);
19 }
20 module.exports = {
21     KthNode : KthNode
22 };