Count longest subsequence in binary tree
Last updated: March 5, 2026
Quick Overview
Given a binary tree, write a function to count the length of the longest subsequence of nodes where each node's value is either 0 or 1. The function should return an integer representing the length of this longest subsequence. The input will be the root node of the binary tree, and the output should be the maximum length of the valid subsequence found.
Salesforce
March 5, 202622
9
2,667 solved
Given a binary tree, write a function to count the length of the longest subsequence of nodes where each node's value is either 0 or 1. The function should return an integer representing the length of this longest subsequence. The input will be the root node of the binary tree, and the output should be the maximum length of the valid subsequence found.
Coding interviews at Salesforce focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you modify your solution to handle streaming input?
- How would your solution change if the input was sorted?
- What is the worst-case input for your solution?
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Problem Analysis
The problem involves finding the longest subsequence of nodes in a binary tree where each node's value is either 0 or 1. This can be approached using Depth-First Search (DFS) since we need to explore ...
Approach
- Define a recursive function that takes a node and a count of the current valid subsequence length as parameters.
- If the current node is null, return the count of the valid subsequence.
- If the...
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