Early September BCG Engineer OA is at it again, this time sharing the real-world experience of one of the participants.
He is an American Master student with a strong data background (two data internships), a good foundation in brushing up on questions, but not too familiar with the Codesignal environment and the OA answering rhythm.
Passed all four questions with flying colors and a very nice final score after our Programhelp mock training!
BCG Engineer OA Overview
Platform: Codesignal
Number of questions: 4
Question Distribution: Array Logic + Hashing + Matrix Processing + Prefix Sums
Difficulty: ⭐⭐⭐⭐⭐☆☆
Q1. Find Peaks in Array
Problem.
Given an array of integers, find all elements that are greater than both their left and right neighbors.
The first and last elements should always be included.
Idea.
Loop through the array from index 1 to n-2.
If arr[i] > arr[i-1] && arr[i] > arr[i+1], include it in the result.
Don't forget to always add the first and last elements.
Time complexity: O(n).
Simple but requires careful boundary handling.
Q2. Book Sections Organizer
Problem.
You are given a list of operations.
switch section_nameadd book_name
Each operation either switches to a new section or adds a book to the current one.
Return the section with the largest number of books at the end.
Idea.
Use a dictionary {section: set_of_books}.
Keep track of the current section while iterating through actions.
- For
add, insert the book into the current section's set. - For
switch, update the current section.
Finally, return the section with the largest set size.
Using a set prevents duplicates - a key detail!
Q3. Matrix Patching and Sorting
Problem.
You are given a large matrix divided into multiple 4×4 blocks.
For each block.
- Fill in the missing numbers (from 1 to 16).
- Sort blocks by the number of missing values.
- Reassemble the blocks into a new full matrix.
Idea.
- Split the matrix into 4×4 blocks.
- Count missing values for each block.
- Fill them up and store
(missing_count, block)in a list. - Sort by
missing_count, then reassemble.
The implementation is tedious but straightforward with nested loops or NumPy arrays.
The test focuses on Data manipulation and logic clarity rather than algorithmic difficulty.
Q4. Longest Subarray under Threshold
Problem.
Given an array and a threshold T, find the longest contiguous subarray satisfying a certain constraint based on sum and T.
Idea.
Using prefix sums, the condition can be transformed into an inequality.P[l] ≥ (P[r+1] - T) / 2
Since all elements are non-negative, prefix sums are monotonic - enabling binary search to find the smallest valid l for each r.
Time complexity: O(n log n).
This problem tests mathematical reasoning and the ability to model inequalities.
Overall Impression
The set of questions reflects BCG's emphasis on "logic and realization".
Instead of algorithmic complexity as in pure SDE, it's about whether you can write clear, maintainable code in a limited amount of time.
The high percentage of applications of matrix chunking and data structures is particularly likely to expose basic weaknesses.
The overall difficulty level is medium to high, so if you familiarize yourself with the Codesignal input and output specifications ahead of time, you'll be able to get a solid score.
BCG Engineer OA common problems
Q1: What is the difference between BCG Engineer OA and traditional SDE OA?
A1: BCG's engineers are more oriented to logic and implementation, not algorithms, but rather the clarity of your code and the completeness of your thoughts.
Q2: What is the difficulty level of the questions in Codesignal?
A2: It is medium to high, Q3 and Q4 are more logical and the first two questions are more basic.
Q3: Is it possible to solve all questions in Python?
A3: Absolutely, Python has a clear advantage in set and matrix manipulation.
Q4：What is the form of mock for Programhelp?
A4: We provide remote non-trace simulation of the actual test, voice real-time reminders + code logic check, to ensure that the pace of the official answer is stable, no error.
Q5: How long does it take to get the result after BCG OA is passed?
A5: Usually notified by email within 5-7 days, sometimes a follow-up VO or case interview will be arranged.
Don't be alone, let the professional assistants accompany you through the OA hurdles
This student, prior to the official test, passed Programhelp 's one-on-one mock training of Codesignal has helped you to get used to the type of questions and the pace of time in Codesignal in advance.
The ability to quickly get into the swing of things and accurately determine the meaning of a question on a formal exam.
Our core assist highlights include:
Remote mock restore scenario: Familiarize yourself in advance with the Codesignal environment, input and output formats, and test point logic;
Real-time voice alerts: Instant prompts to "check boundaries" and "understand the topic in a different dimension" when stuck in logic;
No Trace Online Assist: The whole process is stable and safe, the platform test is not abnormal, and the test point 100% is passed.
Many students from BCG, McKinsey, Bain and other consulting technology positions have successfully obtained offers through similar mock + practice programs.
