230. Kth Smallest Element in a BST

Problem Statement:

Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree.

Example 1:

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

Example 2:

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

Constraints:

The number of nodes in the tree is n.
1 <= k <= n <= 10⁴]
0 <= Node.val <= 10⁴]

Follow up: If the BST is modified often (i.e., we can do insert and delete operations) and you need to find the kth smallest frequently, how would you optimize?

Solution:

java

public class KthSmallestElement {

    public int kthSmallest(TreeNode root, int k) {
        int[] arr = new int[2];
        arr[0] = k;
        kthSmallest(root, arr);
        return arr[1];
    }

    private int[] kthSmallest(TreeNode root, int arr[]) {
        if (root != null) {
            kthSmallest(root.left, arr);
            if (--arr[0] == 0) {
                arr[1] = root.val;
                return arr;
            }
            kthSmallest(root.right, arr);
        }
        return arr;
    }
}

230. Kth Smallest Element in a BST #

Problem Statement: #

Example 1: #

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