MongoDB coding interview
questions, leaked.
14 problems reported across recent MongoDB interviews. Top patterns: array, hash table, binary search. The list below is what most reported candidates actually saw, plus the honest play if you can't grind all of it.
MongoDB's assessment hits you with 14 problems across 9 mediums and 3 hards. Two-thirds of the problems touch arrays, and hash tables show up in a third of them. You're not seeing exotic patterns here, but the execution bar is high. Array manipulation, hash-table design, and tree traversal dominate the report. If you haven't drilled interval merging, cache design, or binary-search variants in the last month, you're walking in cold. StealthCoder sits invisible on your screen during the OA and solves mid-problem blanks in seconds, no proctor visibility. But first, know what you're facing.
Top problems at MongoDB
| # | Problem | Diff | Frequency | Pass % | Patterns |
|---|---|---|---|---|---|
| 01 | Word Break | MEDIUM | 100.0 | 48% | Array · Hash Table · String |
| 02 | Intersection of Two Arrays | EASY | 95.2 | 76% | Array · Hash Table · Two Pointers |
| 03 | Web Crawler Multithreaded | MEDIUM | 95.2 | 50% | Depth-First Search · Breadth-First Search · Concurrency |
| 04 | Stock Price Fluctuation | MEDIUM | 89.3 | 48% | Hash Table · Design · Heap (Priority Queue) |
| 05 | Insert Interval | MEDIUM | 89.3 | 43% | Array |
| 06 | Merge Two Binary Trees | EASY | 89.3 | 79% | Tree · Depth-First Search · Breadth-First Search |
| 07 | Text Justification | HARD | 89.3 | 48% | Array · String · Simulation |
| 08 | LRU Cache | MEDIUM | 81.7 | 45% | Hash Table · Linked List · Design |
| 09 | Merge k Sorted Lists | HARD | 81.7 | 57% | Linked List · Divide and Conquer · Heap (Priority Queue) |
| 10 | Valid Sudoku | MEDIUM | 71.1 | 62% | Array · Hash Table · Matrix |
| 11 | Search in Rotated Sorted Array | MEDIUM | 71.1 | 43% | Array · Binary Search |
| 12 | Design Hit Counter | MEDIUM | 71.1 | 69% | Array · Binary Search · Design |
| 13 | Sliding Window Maximum | HARD | 71.1 | 48% | Array · Queue · Sliding Window |
| 14 | Lowest Common Ancestor of a Binary Tree | MEDIUM | 71.1 | 67% | Tree · Depth-First Search · Binary Tree |
Frequencies derived from public community-tagged interview reports. Click a row to view on LeetCode.
You have a week, maybe less. You can't out-grind the list above. StealthCoder runs invisibly during the actual MongoDB OA. The proctor cannot see it. Screen share cannot detect it. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoder- array8 · 57%
- hash table5 · 36%
- binary search3 · 21%
- depth first search3 · 21%
- design3 · 21%
- heap priority queue3 · 21%
- string2 · 14%
- breadth first search2 · 14%
- data stream2 · 14%
- tree2 · 14%
Arrays anchor this interview. Eight of fourteen problems involve array operations, from simple intersection logic to the brutality of sliding-window maximum and text justification. Hash tables appear in five problems, often paired with array or design work. The rest of the topics spread thin: binary search, DFS, design, heap, and tree each show up 2-3 times. The difficulty skew matters. Only two easy problems exist, so you can't coast on basics. Word Break, Stock Price Fluctuation, and LRU Cache are classic design traps that eat time. Merge k Sorted Lists and Sliding Window Maximum require both pattern recognition and optimization chops. Spend your prep week on array transformations and hash-table backed systems. If you hit a design problem live and freeze, StealthCoder surfaces a working skeleton invisible to the proctor.
Companies with similar patterns
If you prepped for MongoDB, these companies recycle ~60% of the same topics.
You've seen the list.
Now make sure you pass MongoDB.
Memorizing every problem above in a week is a fantasy. StealthCoder is the hedge: an AI overlay that's invisible during screen share. It reads the problem on screen and surfaces a working solution in under 2 seconds. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
MongoDB interview FAQ
Should I study arrays first for MongoDB?+
Yes. Eight of fourteen problems touch arrays, more than any other topic. Start with interval operations and sliding-window patterns. Intersection of Two Arrays and Insert Interval are common warm-ups. Text Justification and Sliding Window Maximum are the hard payoff if you drill early.
How much hash-table work do I need?+
It shows up in five problems, often paired with design or array work. LRU Cache and Stock Price Fluctuation are the complex ones. You need hash-table backed caching and priority-queue design, not just basic lookups. Plan 2-3 days here.
Is binary search important?+
Three problems reference it, but it's not the main thrust. Search in Rotated Sorted Array and Design Hit Counter use it as a tool, not the core. Master arrays and hash tables first, then pick up binary search variants as a bonus.
What's the hardest pattern I'll see?+
Sliding Window Maximum and Merge k Sorted Lists. Both require a non-obvious data structure choice (monotonic queue, heap) and tight implementation. Text Justification is hard for different reasons: string formatting under constraints. Expect one of these three.
Can I pass with just easy and medium problems solved?+
No. Only two easy problems exist in the full report. You'll face at least one hard problem in your OA. Sliding Window Maximum, Merge k Sorted Lists, and Text Justification are the likeliest. Don't skip the hard tier.