GitHub Coding Interview Questions
26 GitHub coding interview problems with full optimal solutions — 12 easy, 10 medium, 4 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an GitHub interviewer values, and a FAQ section.
Showing 26 problems of 26
- #1easyfoundational
1. Two Sum
Find indices of two numbers in an array that sum to a target — GitHub uses this to gauge hash-map intuition before diving into Git ref lookup problems.
- #2easyfoundational
2. Valid Parentheses
Determine if a string of brackets is balanced — GitHub uses this as a warm-up before diving into nested merge conflict markers and diff hunk delimiters.
- #3easyfoundational
3. Merge Two Sorted Lists
Merge two sorted linked lists into one sorted list — GitHub treats this as the toy version of merging two sorted commit-date streams during git log --merge.
- #4easyfoundational
4. Remove Duplicates from Sorted Array
Remove duplicates in-place from a sorted array — GitHub uses this as the entry-level analogue to dedup-ing sorted SHA streams in the packfile delta index.
- #5easyfoundational
5. Remove Element
Remove all occurrences of a value from an array in-place — GitHub's lead-in to pruning broken refs from a packed-refs file without reallocating.
- #6easyfoundational
6. Search Insert Position
Return the index at which a target would be inserted in a sorted array — GitHub's warm-up for the binary search inside the pack-index .idx fan-out table.
- #7easyfoundational
7. Maximum Subarray
Find the contiguous subarray with the largest sum — GitHub uses this Kadane warmup before stepping into hunk-coalescing scoring in their diff renderer.
- #8easyfoundational
8. Plus One
Increment a number represented as a digit array by one — GitHub's tiny entry to BigInt carry handling, mirroring the version-counter bump in tag-name auto-increment scripts.
- #9easyfoundational
9. Merge Sorted Array
Merge two sorted integer arrays in place into nums1 — GitHub's setup for the three-way merge core: writing from the back to avoid clobbering unread input.
- #10easyfoundational
10. Binary Tree Inorder Traversal
Return the inorder traversal of a binary tree's node values — GitHub's lead-in to traversing the parent-DAG of a commit history in chronological order.
- #11easyfoundational
11. Same Tree
Determine if two binary trees are identical — GitHub's stand-in for SHA-equality checks across two commit subtrees in a fast-forward verification.
- #12mediumfoundational
12. Number of Islands
BFS/DFS grid traversal that mirrors how GitHub models repository dependency graphs and connected component analysis.
- #13mediumfoundational
13. Clone Graph
Deep-clone a connected undirected graph using BFS/DFS, directly analogous to forking a repository and cloning its entire commit DAG.
- #14mediumfoundational
14. Course Schedule
Topological sort / cycle detection on a directed graph, directly modeling how GitHub Actions resolves job dependencies and detects circular workflow references.
- #15mediumfoundational
15. Longest Common Subsequence
Classic DP problem that underlies git diff and merge algorithms used daily at GitHub to compute edit distances between file versions.
- #16mediumfoundational
16. Pacific Atlantic Water Flow
Multi-source BFS/DFS on a grid to find cells reachable from both boundaries, testing bidirectional graph traversal skills GitHub values for diff and merge reachability.
- #17mediumfoundational
17. Implement Trie (Prefix Tree)
Build a trie supporting insert, search, and startsWith — the data structure behind GitHub's code search autocomplete and repository name prefix matching.
- #18mediumfoundational
18. Word Search
Backtracking DFS on a grid to find a word path, testing the same traversal and backtracking patterns used in code-search substring matching across file content.
- #19mediumfoundational
19. Find All Anagrams in a String
Sliding window with character frequency maps to find all anagram start indices — a pattern used in GitHub's fuzzy file-name and diff-string search.
- #20hardfoundational
20. Minimum Window Substring
Variable sliding window to find the smallest substring containing all target characters — the canonical string-processing hard problem GitHub tests in senior-level loops.
- #21hardfoundational
21. Serialize and Deserialize Binary Tree
Design a codec to convert a binary tree to/from a string, mirroring how GitHub serializes ASTs and repository tree structures for storage and wire transfer.
- #22easyfoundational
22. Symmetric Tree
Check whether a binary tree is a mirror of itself using recursive or iterative paired traversal, a BFS/DFS tree skill GitHub tests in screening rounds.
- #23mediumfoundational
23. LRU Cache
Design an O(1) get/put LRU cache using a doubly-linked list plus hashmap — the exact caching strategy used in GitHub's object store and pack-file cache layers.
- #24hardfoundational
24. Merge K Sorted Lists
Merge k sorted linked lists into one sorted list using a min-heap, analogous to how GitHub merges multiple sorted commit streams from different remotes during a fetch.
- #25mediumfoundational
25. Max Area of Island
Find the largest connected component in a binary grid using DFS — the same connected-components analysis used when GitHub calculates the largest contiguous change region in a pull request diff.
- #26hardfoundational
26. Trapping Rain Water
Compute water trapped between bars using two-pointer or stack techniques — a classic hard problem GitHub includes in senior engineer interviews to test array reasoning under constraints.
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