230. 二叉搜索树中第K小的元素

 1 public class Kthsmallest {
 2     static class TreeNode {
 3         int val;
 4         TreeNode left;
 5         TreeNode right;
 6         TreeNode(int X) {
 7             val = x;
 8         }
 9     }
10     private int count = 0;
11     private int val;
12     public int kthsmallest(TreeNode root,int k) {
13         inOrder(root,k);
14         return val;
15     }    
16     public void inOrder(TreeNode node,int k) {
17         if(node == null) {
18             return;
19         }
20         inOrder(node.left,k);
21         count++;
22         if(count == k) {
23             val = node.val;
24             return;
25         }
26         inOrder(node.right,k);
27     }
28 }