This Meta interview round featured two challenging problems. One tested careful handling of pointers and traversal, while the other focused on graph algorithms and optimization. With CSOahelp providing real-time full answers, the candidate was able to stay calm, structured, and convincing throughout.
Problem 1: Binary Tree to Circular Doubly Linked List
Problem: Given a binary tree, convert it in-place into a circular doubly linked list, following the in-order traversal order.
For example:
Solution approach (reproduced in real time via CSOahelp):
This is essentially a tree-to-list conversion problem. The key is an in-order traversal with pointer stitching.
Maintain a prev pointer as you traverse. When visiting a node, connect it with prev in both directions.
At the end, connect the head and tail to make the list circular.
Edge cases:
Empty tree → return null.
Single node → point to itself both ways.
Complexity:
Each node is visited once → O(n) time.
Only constant extra space for pointers (O(1)), or O(h) if recursion stack counts, where h is tree height.
The candidate restated these points clearly, giving the impression of deep mastery.
Problem 2: Shortest Path in a Maze
Problem: Given a maze represented as a 2D array, find the shortest path from the top-left corner to the bottom-right corner. 0 = open path, 1 = wall.
Solution approach (again streamed directly via CSOahelp):
This is a shortest path problem in an unweighted grid → use BFS.
Start from (0,0), expand neighbors in four directions, and stop when reaching (n-1, m-1).
Maintain a parent map to reconstruct the path once the exit is found.
Complexity:
Time: O(n·m) for an n×m grid.
Space: O(n·m) for the queue and visited set.
Optimization (to impress the interviewer):
Use bidirectional BFS from both start and end, meeting in the middle.
Use bit-level compression to reduce visited array memory usage.
When the interviewer pushed on optimization, the candidate — supported by CSOahelp’s real-time notes — responded smoothly: “The asymptotic complexity doesn’t change, but constants improve significantly, which matters in large-scale mazes.”
Why CSOahelp Was the Game-Changer
These two problems, taken together, demand not only correctness but also completeness: handling edge cases, explaining complexity, and offering optimizations. Left alone, a candidate might hesitate or miss important details under pressure.
But here, CSOahelp delivered the full, annotated solutions in real time:
Opening clarifications to avoid pitfalls.
Step-by-step algorithm descriptions.
Complexity analysis, phrased succinctly.
Extensions and optimizations to show depth.
All the candidate had to do was reproduce the reasoning naturally. To the interviewer, it looked like a confident, layered answer. In reality, CSOahelp was ensuring no step was forgotten, no edge case missed.
By the end, the candidate had demonstrated not just the ability to code, but the ability to present solutions like an engineer who thinks systematically and communicates clearly — exactly what Meta is looking for.
If you’re preparing for algorithm and system design interviews at Apple, Meta, TikTok, etc., but aren’t sure how to break down problems and handle edge cases, get North American interview secrets. We also offer interview proxy, interview assistance, OA writing, and more to help you land your dream job sooner~
