Zendesk Senior Software Engineer Interview Questions and Answers

Q1. Find longest palindromic substring in a given string.
Ans. 
Use dynamic programming to find the longest palindromic substring in a given string.
• Iterate through the string and expand around each character to find palindromes.

• Store the length of the longest palindrome found so far.

• Return the substring based on the start and end indices of the longest palindrome.
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Q2. How to serialize and deserialise a tree
Ans. 
To serialize and deserialize a tree, use a recursive approach to traverse the tree and store the data in a suitable format.
• Use pre-order traversal to serialize the tree by storing the node values in a list or string.

• For deserialization, reconstruct the tree by recursively building nodes from the serialized data.

• Consider using JSON or XML format for serialization to easily store and retrieve tree structure.
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Q3. Find if a given regex (containing ., * and lower case english chars) matches a given string.
Ans. 
Use regex library to match given regex with string.
• Use a regex library like re in Python to match the given regex with the string.

• Check if the regex matches the string using the library functions.

• Handle cases where the regex contains special characters like . and * appropriately.
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Q4. Explain about throttling and implement throttle function.
Ans. 
Throttling is a technique used to control the rate of requests sent to a server.
• Throttling helps prevent server overload by limiting the number of requests processed at a time.

• Implementing a throttle function involves setting a maximum request rate and delaying excess requests.

• Example: Implementing a throttle function in a web application to limit the number of API calls made to a third-party service.

• Example: Throttlin...read more
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Q1. Find squares of elements in a sorted array and return the sorted response.
Ans. 
Sort the squares of elements in a sorted array and return the sorted response.
• Iterate through the array and square each element.

• Store the squared values in a new array.

• Sort the new array and return it.
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Q2. Write a short promise example and implement your own promise
Ans. 
A promise is a commitment to do something in the future, typically used for asynchronous operations in JavaScript.
• Promises are used to handle asynchronous operations in JavaScript.

• They represent a value that may be available now, in the future, or never.

• Promises have three states: pending, fulfilled, or rejected.

• Example: new Promise((resolve, reject) => { setTimeout(() => resolve('Done!'), 1000); });
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Q3. Explain event loop, what are different types of queues in event loop
Ans. 
Event loop is a mechanism that allows for asynchronous execution of code by managing the order of events in a single thread.
• Event loop continuously checks the call stack for any functions that need to be executed, and processes them in a non-blocking manner.

• Different types of queues in event loop include microtask queue (Promise callbacks), macrotask queue (setTimeout, setInterval callbacks), and animation frame queue
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Q4. What is virtual DOM and why its faster
Ans. 
Virtual DOM is a lightweight copy of the actual DOM, used to improve performance by minimizing direct manipulation of the real DOM.
• Virtual DOM is a concept used in frameworks like React to optimize rendering performance.

• Changes are first made to the virtual DOM, which is then compared to the real DOM to identify the minimal updates needed.

• This approach reduces the number of actual DOM manipulations, resulting in faster...read more
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Q1. Opps, overloading and overriding, factory n singleton patteren
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Q2. Collections HashMap internal working
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Q1. Write polyfill for array map
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Q1. Java 8 and related programming questions springboot microservices details about project
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Q2. Kafka questions and use case
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Q3. API springboot application development
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Q4. Ci cd and cloud
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Q1. Hr related question
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Q1. Get minimum from stream. Query based.
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Q2. Minimum number of platforms for trains. Arrival n departure time is given.
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Q1. Difference between abstract class and interface?
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Q2. Explain OOP in C#?
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A code to identify errors and write Junit. Optimise the code as well.

Q1. Stacks using queue
Ans. 
Implementing a stack using two queues
• Use two queues to simulate a stack

• Push operation: Enqueue the element to queue 1

• Pop operation: Dequeue all elements from queue 1 to queue 2, dequeue the last element from queue 1, then swap the queues

• Top operation: Return the front element of queue 1

• Example: Push 1, 2, 3 - Queue 1: [1, 2, 3], Queue 2: []

• Example: Pop - Queue 1: [1, 2], Queue 2: [3]
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Q2. BFS and Knapsack problem, previous project experience
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Full stack question with java and angular and sql

Case study on project