Kth Smallest Element In a Bst

Asked byUberAmazonFacebookMicrosoftLinkedIn

Problem

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

Examples

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

1 <= k <= number of nodes in the tree.

Solve it in the editor. Sign in free to run your Python or JavaScript against test cases, get a verdict, and track your attempts.

Solve on FeatCode →

How to approach it: the Trees pattern

A tree is a hierarchical structure where each node has at most a fixed number of children (two, for binary trees). Almost every tree problem reduces to a traversal — decide what order you visit nodes in, and what you do at each one.

Look for this pattern when

The problem is naturally recursive: "the answer for this tree depends on the answer for its subtrees."
You need level-by-level information (BFS) versus depth-first structural information (DFS).

Read the full Trees guide →

Video walkthroughs

Original problem on LeetCode ↗