Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.
Note: You may assume k is always valid, 1 ≤ k ≤ BST's total elements.Example 1:Input: root = [3,1,4,null,2], k = 1 3 / \ 1 4 \ 2Output: 1
Example 2:
Input: root = [5,3,6,2,4,null,null,1], k = 3 5 / \ 3 6 / \ 2 4 / 1Output: 3
Follow up:
What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?难度：medium
题目：给定二叉搜索树，找出其值第K小的结点。
思路：中序遍历
Runtime: 0 ms, faster than 100.00% of Java online submissions for Kth Smallest Element in a BST.
Memory Usage: 38.9 MB, less than 19.71% of Java online submissions for Kth Smallest Element in a BST./** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public int kthSmallest(TreeNode root, int k) { int[] result = {root.val}; kthSmallest(root, k, new int[1], result); return result[0]; } public void kthSmallest(TreeNode root, int k, int[] count, int[] result) { if (root == null || count[0] >= k) { return; } kthSmallest(root.left, k, count, result); count[0]++; if (count[0] == k) { result[0] = root.val; return; } kthSmallest(root.right, k, count, result); }}