Recursive Inorder Traversal1
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29/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public ArrayList<Integer> inorder(TreeNode root, ArrayList<Integer> arr) {
if (root == null) return arr;
inorder(root.left, arr);
arr.add(root.val);
inorder(root.right, arr);
return arr;
}
public int kthSmallest(TreeNode root, int k) {
ArrayList<Integer> nums = inorder(root, new ArrayList<Integer>());
return nums.get(k - 1);
}
}