10+ ServiceNow Senior Software Engineer Interview Questions and Answers

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 (requestAnimationFrame callbacks).

Minimum 2 platforms required for a railway station.

• At least 2 platforms are required for trains to arrive and depart simultaneously.

• Additional platforms may be required based on the frequency of trains and passenger traffic.

• Platforms should be long enough to accommodate the longest trains that will use the station.

• Platforms should also have appropriate facilities for passengers, such as seating, shelter, and signage.

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.

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.

Find set of numbers from an array that can form nearest sum to the given number.

• Sort the array in ascending order

• Use two pointers approach to find the nearest sum

• Return the set of numbers

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.

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: Throttling the rate of data transfer in a network to prevent conges...read more

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); });

The problem is to find the least cost to travel from source to destination using dynamic programming.

• Use dynamic programming to solve the problem

• Create a 2D array to store the minimum cost to reach each cell

• Fill the array using the recurrence relation: minCost[i][j] = cost[i][j] + min(minCost[i-1][j], minCost[i][j-1], minCost[i-1][j-1])

• The final answer will be stored in minCost[m][n], where m and n are the coordinates of the destination

• Example: Given a grid with costs to trav...read more

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.

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 rendering.

• Example: React uses virtual DOM to efficiently ...read more

Level order traversal of Binary tree

• Use a queue to traverse the tree level by level

• Enqueue the root node and then dequeue it and enqueue its children

• Repeat until the queue is empty

Detect if two circular linked lists overlap

• Traverse both lists and check if they have the same tail node

• If they have different tail nodes, they do not overlap

• If they have the same tail node, check if they intersect at any point

• Use Floyd's cycle-finding algorithm to detect intersection point

Trapping Rain Water Problem

• The problem involves calculating the amount of water trapped between bars in a histogram

• The solution involves finding the maximum height of bars on both sides of each bar and subtracting the height of the bar itself

• This can be done using two arrays to store the maximum height of bars on the left and right side of each bar