/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int count = 0;
    int result = Integer.MIN_VALUE;

    public int kthSmallest(TreeNode root, int
 
 k) {
        traverse(root, k);
        return result;
    }

    public void traverse(TreeNode root, int k) {
        if(root == null) return;
        traverse(root.left, k);
        count++;
        if(count == k) result = root.val;
        traverse(root.right, k);       
    }
}

劍指offer-二叉查找樹的第 K 個結點