Problem database last updated: June 20, 2025
20 problems · 2 Easy, 9 Medium, 9 Hard · Ranked #91 of 458
2 Easy
10% · avg 23%
9 Medium
45% · avg 59%
9 Hard
45% · avg 18%
Based on 20 reported problems, Dropbox interviews are significantly harder than average - 45% Hard vs 18% across all companies.
Compared to the industry average, Dropbox puts unusual emphasis on union-find (20% of problems, 6.8x the industry average), trie (10% of problems, 3.8x the industry average), simulation (15% of problems, 3.5x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are array (80%), hash-table (50%), string (35%), depth-first-search (20%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Simple Bank System You have been tasked with writing a program for a popular bank that will automate all its incoming transactions (transfer, deposit, and withdraw). The bank has... | Medium | Very Likely | arrayhash-tabledesign | Solve |
Find Duplicate File in System Given a list paths of directory info, including the directory path, and all the files with contents in this directory, return all the duplicate files in the fil... | Medium | Very Likely | arrayhash-tablestring | Solve |
Game of Life According to Wikipedia's article: "The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway... | Medium | Very Likely | arraymatrixsimulation | Solve |
Two Sum Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target. | Easy | Very Likely | arrayhash-map | Solve |
Median of Two Sorted Arrays Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. | Hard | Very Likely | arraybinary-searchdivide-and-conquer | Solve |
Letter Combinations of a Phone Number Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order. | Medium | Very Likely | hash-tablestringbacktracking | Solve |
Word Break II Given a string s and a dictionary of strings wordDict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possi... | Hard | Very Likely | arrayhash-tablestring | Solve |
Grid Illumination There is a 2D grid of size n x n where each cell of this grid has a lamp that is initially turned off. | Hard | Very Likely | arrayhash-table | Solve |
Minimize Malware Spread You are given a network of n nodes represented as an n x n adjacency matrix graph, where the ith node is directly connected to the jth node if graph[i][j] == 1. | Hard | Very Likely | arrayhash-tabledepth-first-search | Solve |
Minimize Malware Spread II You are given a network of n nodes represented as an n x n adjacency matrix graph, where the ith node is directly connected to the jth node if graph[i][j] == 1. | Hard | Very Likely | arrayhash-tabledepth-first-search | Solve |
Seat Reservation Manager Design a system that manages the reservation state of n seats that are numbered from 1 to n. | Medium | Very Likely | designheap-priority-queue | Solve |
Design a Text Editor Design a text editor with a cursor that can do the following: | Hard | Very Likely | linked-liststringstack | Solve |
Check If It Is a Good Array Given an array nums of positive integers. Your task is to select some subset of nums, multiply each element by an integer and add all these numbers. The array i... | Hard | Very Likely | arraymathnumber-theory | Solve |
Word Pattern Given a pattern and a string s, find if s follows the same pattern. | Easy | Very Likely | hash-tablestring | Solve |
Number of Valid Words for Each Puzzle With respect to a given puzzle string, a word is valid if both the following conditions are satisfied: | Hard | Very Likely | arrayhash-tablestring | Solve |
Max Area of Island You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume al... | Medium | Very Likely | arraydepth-first-searchbreadth-first-search | Solve |
Guess the Word You are given an array of unique strings words where words[i] is six letters long. One word of words was chosen as a secret word. | Hard | Likely | arraymathstring | Solve |
Merge Intervals Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cove... | Medium | Likely | arraysorting | Solve |
Top K Frequent Elements Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order. | Medium | Likely | arrayhash-tabledivide-and-conquer | Solve |
Number of Islands Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands. | Medium | Likely | arraydepth-first-searchbreadth-first-search | Solve |
Simple Bank System
SolveYou have been tasked with writing a program for a popular bank that will automate all its incoming transactions (transfer, deposit, and withdraw). The bank has...
Find Duplicate File in System
SolveGiven a list paths of directory info, including the directory path, and all the files with contents in this directory, return all the duplicate files in the fil...
Game of Life
SolveAccording to Wikipedia's article: "The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway...
Two Sum
SolveGiven an array of integers nums and an integer target, return the indices of the two numbers that add up to target.
Median of Two Sorted Arrays
SolveGiven two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.
Letter Combinations of a Phone Number
SolveGiven a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
Word Break II
SolveGiven a string s and a dictionary of strings wordDict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possi...
Grid Illumination
SolveThere is a 2D grid of size n x n where each cell of this grid has a lamp that is initially turned off.
Minimize Malware Spread
SolveYou are given a network of n nodes represented as an n x n adjacency matrix graph, where the ith node is directly connected to the jth node if graph[i][j] == 1.
Minimize Malware Spread II
SolveYou are given a network of n nodes represented as an n x n adjacency matrix graph, where the ith node is directly connected to the jth node if graph[i][j] == 1.
Seat Reservation Manager
SolveDesign a system that manages the reservation state of n seats that are numbered from 1 to n.
Design a Text Editor
SolveDesign a text editor with a cursor that can do the following:
Check If It Is a Good Array
SolveGiven an array nums of positive integers. Your task is to select some subset of nums, multiply each element by an integer and add all these numbers. The array i...
Word Pattern
SolveGiven a pattern and a string s, find if s follows the same pattern.
Number of Valid Words for Each Puzzle
SolveWith respect to a given puzzle string, a word is valid if both the following conditions are satisfied:
Max Area of Island
SolveYou are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume al...
Guess the Word
SolveYou are given an array of unique strings words where words[i] is six letters long. One word of words was chosen as a secret word.
Merge Intervals
SolveGiven an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cove...
Top K Frequent Elements
SolveGiven an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.
Number of Islands
SolveGiven an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Dropbox interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Dropbox interviews focus heavily on array, hash-table, string 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. Dropbox 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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Dropbox has been reported to ask 20 distinct coding problems. The most common topics are array, hash-table, string. 2 are Easy difficulty, 9 are Medium, and 9 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 20 reported problems, Dropbox interviews are significantly harder than average - 45% Hard vs 18% across all companies. 45% 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, string. 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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