leetcode KthSmallestElementinaBST
z
 2019-04-09 10:36:27   
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
import utils.TreeNode;

import java.util.ArrayList;

public class KthSmallestElementinaBST {
    public int kthSmallest(TreeNode root, int k) {
        ArrayList<Integer> l  = new ArrayList<>();
        helper(l, root);
        return l.get(k-1);
    }
    public void helper(ArrayList<Integer> l, TreeNode root) {
        if (root == null)
            return ;
        helper(l, root.left);
        l.add(root.val);
        helper(l, root.right);
    }
}