Brex Coding Interview Questions
25 Brex coding interview problems with full optimal solutions — 13 easy, 9 medium, 3 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Brex interviewer values, and a FAQ section.
Showing 25 problems of 25
- #1easyfoundational
1. Two Sum
Given an array of integers and a target, return indices of two numbers that add to the target.
- #2easyfoundational
2. Valid Parentheses
Determine if a string of brackets is properly opened and closed in the correct order.
- #3easyfoundational
3. Merge Two Sorted Lists
Merge two sorted linked lists into one sorted list by splicing nodes together.
- #4easyfoundational
4. Remove Duplicates from Sorted Array
Remove duplicates in-place from a sorted array and return the new length.
- #5easyfoundational
5. Remove Element
Remove all occurrences of a value in-place from an array and return the new length.
- #6easyfoundational
6. Search Insert Position
Return the index where a target should be inserted in a sorted array to keep it sorted.
- #7easyfoundational
7. Maximum Subarray
Find the contiguous subarray with the largest sum and return that sum.
- #8easyfoundational
8. Plus One
Increment an integer represented as a digit array by one and return the resulting digits.
- #9easyfoundational
9. Merge Sorted Array
Merge two sorted integer arrays in-place such that the result is also sorted.
- #10easyfoundational
10. Binary Tree Inorder Traversal
Return the inorder (left, root, right) traversal of a binary tree's node values.
- #11easyfoundational
11. Same Tree
Determine whether two binary trees are structurally identical with the same values.
- #12mediumfoundational
12. Maximum Product Subarray
Find the contiguous subarray with the largest product — tests dynamic programming with sign-flip tracking, relevant to multi-currency gain/loss computations at Brex.
- #13mediumfoundational
13. Find Minimum in Rotated Sorted Array
Locate the minimum element in a rotated sorted array in O(log n) — tests binary search intuition commonly seen in Brex's infrastructure and data pipeline rounds.
- #14mediumfoundational
14. Number of Islands
Count connected land regions in a 2D grid using BFS or DFS — a graph traversal staple that Brex uses to assess structured problem decomposition skills.
- #15easyfoundational
15. Reverse Linked List
Reverse a singly linked list iteratively or recursively — a fundamental pointer-manipulation problem that Brex uses as a warm-up in onsite coding screens.
- #16mediumfoundational
16. Course Schedule
Detect a cycle in a directed graph of course prerequisites — directly mirrors approval-chain and spend-policy dependency validation at Brex.
- #17mediumfoundational
17. Implement Trie (Prefix Tree)
Build a prefix tree supporting insert, search, and startsWith — tests data structure design skills relevant to Brex's merchant category autocomplete and rules-engine keyword matching.
- #18mediumfoundational
18. Coin Change
Find the fewest coins to make a target amount — a classic unbounded knapsack DP that Brex maps to spend-limit decomposition and multi-currency rounding problems.
- #19mediumfoundational
19. Longest Increasing Subsequence
Find the length of the longest strictly increasing subsequence — a DP / patience-sort problem that Brex interviewers use to test algorithmic depth and optimization awareness.
- #20hardfoundational
20. Trapping Rain Water
Calculate how much water can be trapped between elevation bars — a two-pointer / stack classic that Brex uses to evaluate array reasoning under tight complexity constraints.
- #21mediumfoundational
21. Word Break
Determine whether a string can be segmented into dictionary words — a DP string problem Brex applies to category-keyword parsing in its rules engine.
- #22hardfoundational
22. Median of Two Sorted Arrays
Find the median of two sorted arrays in O(log(m+n)) — a binary search on partition problem that Brex uses to assess candidates' ability to handle ordered financial data sets efficiently.
- #23easyfoundational
23. Contains Duplicate
Detect whether any value appears at least twice in an array — a hash set warm-up that Brex uses to establish baseline data structure fluency.
- #24mediumfoundational
24. Product of Array Except Self
Return an output array where each element is the product of all other elements — a prefix/suffix product trick Brex tests in financial aggregation and ledger balance contexts.
- #25hardfoundational
25. Serialize and Deserialize Binary Tree
Encode a binary tree to a string and decode it back — a design + traversal problem Brex uses to probe candidates' thinking about data persistence and approval-hierarchy snapshots.