GitLab Coding Interview Questions
25 GitLab coding interview problems with full optimal solutions — 15 easy, 7 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 GitLab interviewer values, and a FAQ section.
- #1easyfoundational
1. Two Sum
Find two indices in an array whose values sum to a target.
- #2easyfoundational
2. Valid Parentheses
Validate that a string of brackets is properly nested and closed in order.
- #3easyfoundational
3. Merge Two Sorted Lists
Merge two sorted singly linked lists into one sorted list.
- #4easyfoundational
4. Remove Duplicates from Sorted Array
In-place deduplicate a sorted array and return the new length.
- #5easyfoundational
5. Remove Element
Remove all occurrences of a value from an array in-place.
- #6easyfoundational
6. Search Insert Position
Find the index where a target should be inserted in a sorted array.
- #7easyfoundational
7. Plus One
Increment a large integer represented as a digit array by one.
- #8easyfoundational
8. Merge Sorted Array
Merge two sorted integer arrays in-place into the first one.
- #9easyfoundational
9. Binary Tree Inorder Traversal
Return the in-order traversal of a binary tree's node values.
- #10easyfoundational
10. Same Tree
Check whether two binary trees are structurally and value-wise identical.
- #11easyfoundational
11. Maximum Depth of Binary Tree
Return the maximum depth of a binary tree from root to deepest leaf.
- #12easyfoundational
12. Best Time to Buy and Sell Stock
Find the maximum profit from a single buy/sell of one stock, given a daily price array.
- #13easyfoundational
13. Single Number
Find the element that appears exactly once in an array where every other element appears twice.
- #14easyfoundational
14. Linked List Cycle
Detect whether a singly linked list contains a cycle using O(1) extra memory.
- #15easyfoundational
15. Reverse Linked List
Reverse a singly linked list in place and return the new head.
- #16mediumfoundational
16. Course Schedule
Decide whether a set of courses with prerequisite pairs can be completed — i.e. whether the dependency graph is acyclic.
- #17mediumfoundational
17. Course Schedule II
Return any valid course ordering that satisfies the prerequisite dependencies, or an empty list if the graph has a cycle.
- #18mediumfoundational
18. LRU Cache
Implement a cache with O(1) get and put that evicts the least recently used entry when full.
- #19mediumfoundational
19. Number of Islands
Count connected components of '1' cells in a 2D grid where neighbors are 4-directional.
- #20mediumfoundational
20. Kth Largest Element in an Array
Return the kth largest element of an unsorted array, ideally without fully sorting it.
- #21mediumfoundational
21. Lowest Common Ancestor of a Binary Tree
Find the deepest node that has both p and q as descendants in a binary tree.
- #22mediumfoundational
22. Top K Frequent Words
Return the k most frequent words, breaking frequency ties alphabetically.
- #23hardfoundational
23. Alien Dictionary
Given words sorted by an unknown alphabet, recover any valid alphabet order or return '' if impossible.
- #24hardfoundational
24. Longest Increasing Path in a Matrix
Find the longest strictly increasing path in an integer matrix using 4-directional moves.
- #25hardfoundational
25. LFU Cache
Implement a cache with O(1) get and put that evicts the least frequently used entry, breaking ties by least recently used.