Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Bloomberg SWE interview with a linked list problem that sounds manageable until you actually sit down with it. The recursive structure tripped me up more than I expected.

Questions Asked (1)

Given a doubly linked list where some nodes have a child pointer pointing to another doubly linked list (which can itself have children), flatten the entire structure into a single-level doubly linked list. The traversal order should be depth-first, and all child pointers should be null after flattening.

Algorithms & Data Structures

Author's notes

I got the basic idea pretty fast but then fumbled on the pointer updates.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Use a recursive depth-first traversal that processes each node, and when a child exists, recursively flatten the child list and splice it between the current node and its next node. Update all necessary pointers (next, prev, child) to maintain the doubly linked list structure and set child to null.

Pro tip: Clarify with the interviewer whether recursion depth is a concern; if so, mention an iterative stack-based approach as an alternative. Also, explicitly handle edge cases like empty lists or nodes with no children to demonstrate thoroughness.

1. Understand the problem and constraints

Confirm the input structure, expected output, and any constraints (e.g., recursion depth, memory). Ask clarifying questions about edge cases.

2. Design the recursive approach

Outline a function that traverses the list, and when a child is found, recursively flattens the child list and splices it into the main list.

3. Detail pointer manipulation

Explain how to adjust next, prev, and child pointers: connect current node to child's head, child's tail to current's next, and set child to null.

4. Analyze complexity and edge cases

State time and space complexity (O(n) time, O(d) space for recursion depth d). Discuss handling of empty lists, single nodes, and deep nesting.

5. Consider iterative alternative

Mention that an iterative stack-based approach can avoid recursion overhead, and briefly describe how it would work.

Key Points to Mention

Depth-first traversal order: process child before moving to next sibling.
Pointer updates: ensure prev pointers are correctly set for the spliced segment.
Setting child pointers to null after flattening.
Time complexity O(n) where n is total number of nodes.
Space complexity O(d) for recursion stack, where d is maximum depth of nesting.
Edge cases: empty list, no children, child at tail, multiple levels of nesting.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.