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Leetcode230-kthSmallestElementinaBST

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

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

Example 1:

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Input: root = [3,1,4,null,2], k = 1
   3
  / \
 1   4
  \
   2
Output: 1

Example 2:
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Input: root = [5,3,6,2,4,null,null,1], k = 3
       5
      / \
     3   6
    / \
   2   4
  /
 1
Output: 3

Solution

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int count;
    private int res;
    public int kthSmallest(TreeNode root, int k) {
        count = k;
        inOrder(root);
        return res;
    }
    
    private void inOrder(TreeNode node){
        if (node.left != null) inOrder(node.left);
        count--;
        if (count == 0){
            res = node.val;
            return;
        }
        if (node.right != null) inOrder(node.right);
    }
}