[LeetCode 230] Kth Smallest Element in a BST

Given a binary search tree, write a function kthSmallest to find thekth smallest element in it.

Note: You may assume k is always valid, 1 ≤ k ≤ BST’s total elements.

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?

Hint:

solution:

Inorder traverse, get kth element from that result. complexity is O(n)

public class Solution {List<Integer> path = new ArrayList<>();public int kthSmallest(TreeNode root, int k) {inorder(root);return path.get(k-1);}public void inorder(TreeNode root) {if(root != null){inorder(root.left);path.add(root.val);inorder(root.right);}}}

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