Problem database last updated: June 20, 2025
12 problems · 2 Easy, 7 Medium, 3 Hard · Ranked #127 of 458
2 Easy
17% · avg 23%
7 Medium
58% · avg 59%
3 Hard
25% · avg 18%
Based on 12 reported problems, MongoDB interviews are slightly harder than average - 25% Hard vs 18% across all companies. The majority (58%) of questions are Medium difficulty, which is typical for companies that want to see solid fundamentals without excessive trick questions.
Compared to the industry average, MongoDB puts unusual emphasis on heap-priority-queue (25% of problems, 4.1x the industry average), binary-tree (16.7% of problems, 3.4x the industry average), tree (16.7% of problems, 3x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are array (58.3%), hash-table (41.7%), heap-priority-queue (25%), string (16.7%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Word Break Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words. | Medium | Very Likely | arrayhash-tablestring | Solve |
Intersection of Two Arrays Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any... | Easy | Very Likely | arrayhash-tabletwo-pointers | Solve |
Text Justification Given an array of strings words and a width maxWidth, format the text such that each line has exactly maxWidth characters and is fully (left and right) justifie... | Hard | Very Likely | arraystringsimulation | Solve |
Merge Two Binary Trees You are given two binary trees root1 and root2. | Easy | Very Likely | treedepth-first-searchbreadth-first-search | Solve |
Insert Interval You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and interv... | Medium | Very Likely | array | Solve |
Stock Price Fluctuation You are given a stream of records about a particular stock. Each record contains a timestamp and the corresponding price of the stock at that timestamp. | Medium | Very Likely | hash-tabledesignheap-priority-queue | Solve |
Merge k Sorted Lists You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. | Hard | Very Likely | linked-listdivide-and-conquerheap-priority-queue | Solve |
LRU Cache Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. | Medium | Very Likely | hash-tablelinked-listdesign | Solve |
Search in Rotated Sorted Array There is an integer array nums sorted in ascending order (with distinct values). | Medium | Likely | arraybinary-search | Solve |
Lowest Common Ancestor of a Binary Tree Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. | Medium | Likely | treedepth-first-searchbinary-tree | Solve |
Sliding Window Maximum You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see... | Hard | Likely | arrayqueuesliding-window | Solve |
Valid Sudoku Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: | Medium | Likely | arrayhash-tablematrix | Solve |
Word Break
SolveGiven a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.
Intersection of Two Arrays
SolveGiven two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any...
Text Justification
SolveGiven an array of strings words and a width maxWidth, format the text such that each line has exactly maxWidth characters and is fully (left and right) justifie...
Merge Two Binary Trees
SolveYou are given two binary trees root1 and root2.
Insert Interval
SolveYou are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and interv...
Stock Price Fluctuation
SolveYou are given a stream of records about a particular stock. Each record contains a timestamp and the corresponding price of the stock at that timestamp.
Merge k Sorted Lists
SolveYou are given an array of k linked-lists lists, each linked-list is sorted in ascending order.
LRU Cache
SolveDesign a data structure that follows the constraints of a Least Recently Used (LRU) cache.
Search in Rotated Sorted Array
SolveThere is an integer array nums sorted in ascending order (with distinct values).
Lowest Common Ancestor of a Binary Tree
SolveGiven a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
Sliding Window Maximum
SolveYou are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see...
Valid Sudoku
SolveDetermine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent MongoDB interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
MongoDB interviews focus heavily on array, hash-table, heap-priority-queue problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. MongoDB interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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MongoDB has been reported to ask 12 distinct coding problems. The most common topics are array, hash-table, heap-priority-queue. 2 are Easy difficulty, 7 are Medium, and 3 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 12 reported problems, MongoDB interviews are slightly harder than average - 25% Hard vs 18% across all companies. 58% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: array, hash-table, heap-priority-queue. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
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