Problem database last updated: June 20, 2025
18 problems · 2 Easy, 13 Medium, 3 Hard · Ranked #100 of 458
2 Easy
11% · avg 23%
13 Medium
72% · avg 59%
3 Hard
17% · avg 18%
Based on 18 reported problems, Zopsmart interviews are in line with industry averages - 17% Hard vs 18% overall. The majority (72%) 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, Zopsmart puts unusual emphasis on monotonic-stack (11.1% of problems, 3.8x the industry average), recursion (16.7% of problems, 3.7x the industry average), linked-list (22.2% of problems, 3.1x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are string (50%), array (33.3%), two-pointers (33.3%), linked-list (22.2%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Zigzag Conversion The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better... | Medium | Very Likely | string | Solve |
Trapping Rain Water Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining. | Hard | Very Likely | arraytwo-pointersdynamic-programming | Solve |
Reverse Nodes in Even Length Groups You are given the head of a linked list. | Medium | Very Likely | linked-list | Solve |
Minimum Window Substring Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc... | Hard | Likely | hash-tablestringsliding-window | Solve |
Bulls and Cows You are playing the Bulls and Cows game with your friend. | Medium | Likely | hash-tablestringcounting | Solve |
Fraction Addition and Subtraction Given a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format. | Medium | Likely | mathstringsimulation | Solve |
Remove K Digits Given string num representing a non-negative integer num, and an integer k, return the smallest possible integer after removing k digits from num. | Medium | Likely | stringstackgreedy | Solve |
Reverse Words in a String Given an input string s, reverse the order of the words. | Medium | Likely | two-pointersstring | Solve |
Group Anagrams Given an array of strings strs, group the anagrams together. You can return the answer in any order. | Medium | Likely | arrayhash-tablestring | Solve |
Container With Most Water You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i, 0) and (i, height[i]). | Medium | Likely | arraytwo-pointersgreedy | 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 | Likely | hash-tablestringbacktracking | Solve |
Best Time to Buy and Sell Stock You are given an array prices where prices[i] is the price of a given stock on the ith day. | Easy | Likely | arraydynamic-programming | Solve |
Longest Palindromic Substring Given a string s, return the longest palindromic substring in s. | Medium | Likely | two-pointersstringdynamic-programming | Solve |
Add Two Numbers You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a sing... | Medium | Likely | linked-listmathrecursion | Solve |
Reverse Linked List Given the head of a singly linked list, reverse the list, and return the reversed list. | Easy | Likely | linked-listrecursion | Solve |
3Sum Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0. | Medium | Likely | arraytwo-pointerssorting | Solve |
Sort Colors Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order... | Medium | Likely | arraytwo-pointerssorting | Solve |
Reverse Nodes in k-Group Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list. | Hard | Likely | linked-listrecursion | Solve |
Zigzag Conversion
SolveThe string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better...
Trapping Rain Water
SolveGiven n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Reverse Nodes in Even Length Groups
SolveYou are given the head of a linked list.
Minimum Window Substring
SolveGiven two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc...
Bulls and Cows
SolveYou are playing the Bulls and Cows game with your friend.
Fraction Addition and Subtraction
SolveGiven a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format.
Remove K Digits
SolveGiven string num representing a non-negative integer num, and an integer k, return the smallest possible integer after removing k digits from num.
Reverse Words in a String
SolveGiven an input string s, reverse the order of the words.
Group Anagrams
SolveGiven an array of strings strs, group the anagrams together. You can return the answer in any order.
Container With Most Water
SolveYou are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i, 0) and (i, height[i]).
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.
Best Time to Buy and Sell Stock
SolveYou are given an array prices where prices[i] is the price of a given stock on the ith day.
Longest Palindromic Substring
SolveGiven a string s, return the longest palindromic substring in s.
Add Two Numbers
SolveYou are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a sing...
Reverse Linked List
SolveGiven the head of a singly linked list, reverse the list, and return the reversed list.
3Sum
SolveGiven an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
Sort Colors
SolveGiven an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order...
Reverse Nodes in k-Group
SolveGiven the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Zopsmart interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Zopsmart interviews focus heavily on string, array, two-pointers 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. Zopsmart 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.
Looking for more companies? Browse all 458 companies in our directory, or sharpen your fundamentals with our free data structure visualizers and AI-powered DSA tutor.
Zopsmart has been reported to ask 18 distinct coding problems. The most common topics are string, array, two-pointers. 2 are Easy difficulty, 13 are Medium, and 3 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 18 reported problems, Zopsmart interviews are in line with industry averages - 17% Hard vs 18% overall. 72% 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: string, array, two-pointers. 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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