71 questions · from 8 interviews · 4 asked more than once
Zscaler interview questions
Every question candidates reported from their Zscaler interviews, most frequently asked first. Each links to the write-up it came from, so you can see the round and how it went.
Zscaler coding and DSA questions
- 01
Find Element with Odd Frequency
Find the element in an array that appears an odd number of times.
Easy · Asked 2 times · From Zscaler Developer C Intern Interview Questions
- 02
Sum of Divisors of GCD of Array Elements
Given an array of integers, find the sum of all divisors of the Greatest Common Divisor (GCD) of all elements in the array.
Medium · Asked 2 times · From Zscaler Developer C Intern Interview Questions
- 03
Merge Intervals
Given a collection of intervals, merge all overlapping intervals.
Medium · Asked 2 times · From Zscaler Developer C Intern Interview Questions
- 04
Longest Common Subsequence
Given two strings, find the length of their longest common subsequence.
Medium · Asked 2 times · From Zscaler Developer C Intern Interview Questions
- 05
Implement Rate Limiting with Multiple Criteria
Implement a rate limiting feature that enforces several constraints simultaneously: limit per job effort, limit per user, limit per day, and limit per hour. The solution should correctly track usage across these dimensions and reject requests that exceed any…
- 06
Product of Array Except Self
Given an integer array nums, return an array answer such that answer[i] is the product of all the elements of nums except nums[i]. The solution must run in O(n) time and without using division.
Easy · From Offer | Zscaler Senior Staff SDE Interview Experience | May 2026
- 07
Longest Mountain in Array
Given an integer array arr, return the length of the longest subarray that is a mountain. A mountain is defined as a subarray that strictly increases and then strictly decreases, with at least three elements.
Medium · From Offer | Zscaler Senior Staff SDE Interview Experience | May 2026
- 08
LFU Cache
Design and implement a data structure for a Least Frequently Used (LFU) cache. It should support the operations get(key) and put(key, value). When the cache reaches its capacity, it should evict the least frequently used key. If multiple keys have the same…
Hard · From Offer | Zscaler Senior Staff SDE Interview Experience | May 2026
- 09
Remove Nth Node From End of List
During the first technical interview, I was asked to solve this common Data Structures and Algorithms problem on HackerRank CodePair. The task is to remove the nth node from the end of a given singly linked list.
Medium · From Zscaler SDE Internship Interview Experience (On-campus | CTC: 27 LPA)
- 10
Binary Tree Maximum Path Sum
In the same technical interview, another DSA question involved finding the maximum path sum. This typically refers to finding the path with the largest sum in a binary tree, where a path can start and end at any node.
Hard · From Zscaler SDE Internship Interview Experience (On-campus | CTC: 27 LPA)
- 11
Minimize Sum (Heap Problem)
During the second technical interview, I encountered a problem where the objective was to minimize a sum, and the interviewer specifically mentioned that it was a heap-based question. I could only provide a partial solution.
From Zscaler SDE Internship Interview Experience (On-campus | CTC: 27 LPA)
- 12
Longest Lexicographically Smallest Palindrome from Two Strings
Generate all possible palindromes from two given strings. The challenge is to combine these palindromes to find the longest and lexicographically smallest one.
Medium · From Zscaler | Intern + FTE | Oncampus | 2023
- 13
Asteroid Collision (similar problem)
A data structures and algorithms problem similar to LeetCode's 'Asteroid Collision' problem.
Medium · From Zscaler | Intern + FTE | Oncampus | 2023
- 14
Count Vowel Strings with Adjacency Constraints
Find the number of strings of length n that can be formed using the characters 'a', 'e', 'i', 'o', 'u' such that 'a' can only come after 'e', 'e' can only come after 'i', and similar adjacency constraints.
Medium · From Zscaler | Intern + FTE | Oncampus | 2023
- 15
Complex Queue Problem with Nth State Print & Log Analysis
Implement a solution for a queue problem where the print function was required for the nth state. This problem involved a complex queue and some log analysis mechanism to analyze logs of very large size.
Hard · From Zscaler | Intern + FTE | Oncampus | 2023
- 16
Run Length Encoding in C
Implement Run Length Encoding for a string, strictly in C language.
- 17
Run Length Encoding
Implement the run-length encoding algorithm. Given an input string, return its compressed version. For example, 'AAABBC' should be encoded as 'A3B2C1'. The implementation must be strictly in C language.
Easy · From Zscaler Interview Experience for Developer C Intern
- 18
String Pattern Matching (Rabin-Karp)
Implement a string pattern matching algorithm in C. First, describe the brute force approach with O(N^2) time complexity. Then, explain how to optimize it using an algorithm like Rabin-Karp for better performance.
Medium · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 19
Array vs. Linked List Use Cases
Explain the key differences between arrays and linked lists, focusing on their respective use-cases where each data structure would be more advantageous.
Easy · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 20
Binary Search Time Complexity Proof
Explain the binary search algorithm and provide a mathematical proof for its time complexity.
Easy · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 21
Mathematical Proof of Floyd's Cycle-Finding Algorithm
Provide a mathematical proof for the working of the Hare and Tortoise algorithm (Floyd's cycle-finding algorithm) for detecting cycles in a linked list.
Medium · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 22
C++ Unordered Maps Internal Working and Ordered Map Simulation
Explain the internal working of C++ unorderedmaps , including key hashing (e.g., modulo M), collision handling (e.g., array of linked lists), and rehashing. Then, consider a modified scenario where a very small M is used without rehashing, and the complexity…
Hard · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 23
Implement Custom `malloc` and `free`
Implement custom versions of malloc and free functions in C. Aim for a robust solution with O(1) time complexity.
Hard · From Zscaler | Internship + FTE | Software Developer C/C++ | On-Campus | Bangalore [Offer Accepted]
- 24
DOM Manipulation Coding Challenge
In the first coding round, I was presented with a DOM manipulation question that required passing several test cases. I was able to solve most of it, though one test case failed.
- 25
Remove Duplicates from Array
I was given a DSA question to remove duplicate elements from an array. Although the interviewer wanted the solution in JavaScript, I explained different approaches in C++ and he seemed satisfied. He then explained the JavaScript code to me.
Easy · From ZSCALER | UI DEVELOPER | INTERNSHIP + FTE | SELECTED
Zscaler system design questions
- 01
Design a Large‑Scale Metrics Monitoring and Alerting System
Design a large‑scale metrics monitoring and alerting system for a global microservices architecture. The system must allow engineers to track service health, visualize performance via dashboards, and receive real‑time alerts when anomalies occur. Consider…
Zscaler other questions
- 01
Enable Video Playback after Partial Download
Explain how to make a video playable after a partial download. Discuss techniques for streaming, chunking, handling range requests, and ensuring secure and efficient delivery of video content to the client.
- 02
VPNs: Personal vs. Enterprise & Detailed Workings
Explain the differences between personal and enterprise-level VPNs. Describe the detailed workings of VPNs, including tunneling protocols, encryption, and authentication mechanisms.
- 03
IP Addresses: IPv4 vs. IPv6
Discuss implementations and scenarios involving IP addresses, covering differences between IPv4 and IPv6, their addressing schemes, and requirements.
- 04
OSI Model and Protocols (DNS, DHCP)
Discuss questions related to the OSI model, including protocols like DNS and DHCP, and their functions within the model.
- 05
DoS Attacks and Asymmetric Encryption
Explain Denial of Service (DoS) attacks and the principles behind asymmetric encryption.
- 06
Smart Pointers
Provide an in-depth explanation of smart pointers, highlighting their benefits over traditional pointers, such as automatic memory management and prevention of memory leaks.
- 07
Request/Response Troubleshooting (Machine Down or Port Not Working)
How would you determine if a machine is down or if the port you sent a request to is not working when there is no response?
- 08
Check If Byte Is Set Using Pointer Arithmetic
How would you check if a particular byte is set using pointer arithmetic? Discuss pointer increment, high-level data structures, and hexadecimal addresses.
- 09
ARP Protocol Working
Explain the working of ARP (Address Resolution Protocol) in depth.
- 10
TCP Three-Way & TLS Handshake Protocols
Explain the Three-Way Handshake protocol and extend the discussion to the TLS Handshake protocol.
- 11
TCP vs. UDP Differences & Use Cases
Discuss the differences between TCP and UDP, including their applications and appropriate use cases.
- 12
Implement OOP Concepts (Inheritance, Polymorphism, Virtual Functions, Function Overloading)
Implement various OOP concepts such as inheritance, polymorphism, virtual functions, and function overloading. Be prepared to modify them for different use cases and explain the concepts concretely.
- 13
HTTP vs. HTTPS & TLS Handshake
Explain the differences between HTTP and HTTPS. How does a TLS handshake work?
- 14
Main Function Call & Program Compilation/Interpretation
Who calls the main() function, and what happens during the compilation and interpretation of a program?
- 15
Threads vs. Processes & Scheduling
Discuss threads and processes in depth. Is there thread scheduling or process scheduling? If a single class main() program calls a function, will it involve threads?
- 16
Memory Architecture of a Process
Discuss the memory architecture of a process in depth.
- 17
In-Depth OOP Concepts & Comparison to Procedural Programming
Explain OOP concepts in depth, including the use of abstraction and security aspects. Why is OOP preferred over procedural programming? What were the drawbacks of procedural programming?
- 18
Multithreading in C
Discuss achieving multithreading in C, including memory management aspects handled by the OS.
- 19
C Pointers: Decimal, Hexadecimal & Address Allocation
Discuss C pointers extensively, including decimal and hexadecimal pointers, and their address allocation.
- 20
C Data Structures: Static Integers, 2D Array Memory, Recursion Stack
Discuss static integers, memory allocation for 2D arrays, and how recursion is stored in the stack in C.
- 21
- 22
Process vs. Thread (System Calls, User/Kernel Modes)
Discuss differences between processes and threads, including system call interfaces and user vs. kernel modes.
- 23
Memory Management & Architecture (Threads, Shared Resources, Virtual Memory)
Discuss memory management and architecture, including how threads improve process execution efficiency, common shared vs. non-shared resources, and virtual memory limitations.
- 24
Multiprogramming Scenario: Two 2GB Processes on 3GB, 32-bit
Explain if two 2 GB processes could run concurrently on a 3 GB, 32-bit architecture.
- 25
C++ Compilation, C vs. C++, Custom Mutexes
Discuss the C++ compilation process, differences between C++ and C, and the implementation of custom mutexes.
20 more in the Zscaler write-ups.
Zscaler interview questions FAQ
What questions are asked in Zscaler interviews?
Candidates reported 71 distinct questions across 8 Zscaler interviews. 25 coding and DSA questions, 1 system design questions, 45 other questions.
Which Zscaler interview questions are asked most often?
The most repeated are "Find Element with Odd Frequency" (2 times), "Sum of Divisors of GCD of Array Elements" (2 times), "Merge Intervals" (2 times), "Longest Common Subsequence" (2 times).
How difficult are Zscaler interview questions?
Of the questions candidates rated, 29% were easy, 48% medium and 24% hard.