Is Find Mode in Binary Search Tree easy or hard?

The problem is rated Easy on LeetCode with an acceptance rate around 58%. The HashMap approach is straightforward, while the optimized constant-space solution requires deeper understanding of BST inorder traversal and Morris traversal techniques.

Find Mode in Binary Search Tree Python/Java solution

Python and Java solutions typically perform an inorder traversal and count occurrences. The simple approach stores frequencies in a dictionary or HashMap, while the optimized version tracks counts of consecutive values during traversal and updates the result list dynamically.

How to solve Find Mode in Binary Search Tree in O(n)?

Perform an inorder traversal so values are visited in sorted order. Track the previous value and maintain a running frequency counter for consecutive duplicates. Update the maximum frequency and store values that match it. Each node is processed once, resulting in O(n) time complexity.

What is the best approach for Find Mode in Binary Search Tree?

The optimal approach uses inorder traversal of the BST while counting consecutive values. Because inorder traversal produces sorted values, duplicates appear next to each other, allowing frequency tracking with only a few variables. Using Morris traversal reduces auxiliary space to O(1) while maintaining O(n) time complexity.

Is Find Mode in Binary Search Tree asked at Google/Amazon/Meta?

Binary tree and BST traversal problems frequently appear in interviews at companies like Amazon, Google, and Meta. Variants involving inorder traversal, frequency counting, or BST properties are common in coding interview question sets.

What data structure is used in Find Mode in Binary Search Tree?

The most common implementation uses a hash map to count frequencies during traversal. Optimized solutions rely on the BST property and track counts during inorder traversal without extra data structures, sometimes using Morris traversal to achieve O(1) space.

What is the time complexity of Find Mode in Binary Search Tree?

All efficient solutions run in O(n) time because every node in the tree must be visited at least once. The HashMap counting approach uses O(n) space, while the Morris inorder traversal approach reduces auxiliary space to O(1).

Description Solution Video 10:53

501. Find Mode in Binary Search Tree

Easy59.2% acceptance4 companies

Given the root of a binary search tree (BST) with duplicates, return all the mode(s) (i.e., the most frequently occurred element) in it.

If the tree has more than one mode, return them in any order.

Assume a BST is defined as follows:

The left subtree of a node contains only nodes with keys less than or equal to the node's key.
The right subtree of a node contains only nodes with keys greater than or equal to the node's key.
Both the left and right subtrees must also be binary search trees.

Example 1: