Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Given a list of accounts where each account consists of a name followed by some email addresses, merge these accounts. Two accounts belong to the same person if they have some email common. Note that even if two accounts have the same name, they may belong to different people as people could have the same name. A person can have any number of accounts initially, but all of their accounts have the same name.

Given an array of meeting time intervals intervals where intervals[i] = [starti, endi], return the minimum number of conference rooms required.

The interview included general behavioral and situational questions designed to assess problem-solving skills, teamwork, handling conflict, and career aspirations.

Find the minimum time taken to burn the entire binary tree starting from a given target node.

Given a 2D grid consisting of walls, empty cells, the starting point, keys, and locks. Return the shortest path to get all keys.

Given n jobs where startTime[i], endTime[i], and profit[i] are the start time, end time, and profit of the i-th job, return the maximum profit you can achieve by scheduling jobs such that no two jobs overlap.

Two strings are considered 'close' if you can attain one from the other using two types of operations: 1. Swap any two existing characters. 2. Transform every occurrence of one existing character into another existing character, and vice versa. Return true if they are close, false otherwise.

You are given an integer array matchsticks where matchsticks[i] is the length of the i-th matchstick. You want to use all the matchsticks to form one square. You should not break any single matchstick, but you can link them up, and each matchstick must be used exactly one time. Return true if you can make this square, and false otherwise.

Given an n x n matrix where each of the rows and columns is sorted in ascending order, return the k-th smallest element in the matrix.

You are given n balloons, indexed from 0 to n - 1. Each balloon is painted with a number on it. If you burst balloon i, you will get nums[left] * nums[i] * nums[right] coins. Your goal is to burst all the balloons to get the maximum coins. Assume nums[-1] = nums[n] = 1.

In a group of N people, a celebrity is someone who is known by everyone else but does not know anyone. Find the celebrity if one exists.

Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.

Problem statement from Codeforces problem 1037/D, related to tree traversals.

Given a string, find the minimum number of swaps required to make it a palindrome.

Given a binary tree, find the sum of all nodes at the deepest level.

A problem about maximizing total damage with spell casting. I had to devise a strategy, possibly using sliding window or dynamic programming, to balance choices and constraints.

You are given an array of stones where stones[i] = [ri, ci] represents the location of a stone on a 2D plane. You can remove a stone if and only if it shares the same row or column as another stone that has not been removed. Return the maximum number of stones that you can remove.

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.

Given a binary tree, print the nodes in 'left view' order (first node at each level from the left side).

Given the root of a binary tree, the value of a target node, and an integer k, return an array of the values of all nodes that have a distance k from the target node.

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the next level and alternate between).

A problem solvable using a monotonic stack. The interviewer modified the question multiple times during the interview. I solved the initial problem and its first modification.

Given an unsorted integer array nums, return the smallest missing positive integer.

Given an m x n integers matrix, return the length of the longest increasing path in the matrix. From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary (i.e., no wrap-around is allowed).

Implement the CBTInserter class. The question specifically asked for an O(log n) solution for insertion, though I could only achieve O(n).

You are given an array of people, people, as people[i] = [hi, ki]. hi is the height of the i-th person, and ki is the number of people in front of the i-th person who have a height greater than or equal to hi. Reconstruct the queue.

The thief has found himself a new place for his thievery again. There is only one entrance to this area, called root. Besides the root, each house has one and only one parent house. After a tour, the smart thief realized that all houses in this place form a binary tree. It will automatically contact the police if two directly-linked houses were robbed on the same night. Determine the maximum amount of money the thief can rob tonight without alerting the police.

Given a tree with n nodes labeled from 0 to n - 1, and parent[i] denotes the parent of i-th node. Find the k-th ancestor of a given node.

You are given an m x n grid representing a map of bricks. A brick is at grid[i][j] = 1 and an empty cell is at grid[i][j] = 0. You are also given an array hits, where hits[i] = [rowi, coli] indicates a brick (if exists) at that position is removed. We need to find the number of bricks that will fall after each hit.

A problem related to finding the convex hull of a set of points.

Write a function that generates random points within a circle with equal probability distribution.

There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function, nums is possibly rotated at an unknown pivot index k. Given the array nums after the rotation and an integer target, return the index of target if it is in nums, or -1 otherwise.

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. The path does not necessarily need to pass through the root. The path sum is the sum of the node's values in the path. Given the root of a binary tree, return the maximum path sum of any non-empty path.

Given an array of integers, count the maximum number of integers you can add such that at any point, the cumulative sum from left to right never goes negative. The question was presented in a scenario.

There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given an array edges of length n - 1, where edges[i] = [ai, bi] indicates that there is an edge between nodes ai and bi. Return an array answer of length n where answer[i] is the sum of the distances between node i and all other nodes in the tree.

You are given an m x n grid where each cell can have one of three values: 0 representing an empty cell, 1 representing a fresh orange, or 2 representing a rotten orange. Every minute, any fresh orange that is 4-directionally adjacent to a rotten orange becomes rotten. Return the minimum number of minutes that must elapse until no fresh oranges remain. If this is impossible, return -1.

A greedy problem similar to typical meeting scheduling or interval problems.

A problem that can be solved using a monotonic stack, similar to finding the next greater element.

You are given an m x n integer matrix grid where grid[i][j] is either 0 (empty) or 1 (obstacle). You can move up, down, left, or right. You are also given an integer k. Return the minimum number of steps to walk from (0, 0) to (m - 1, n - 1) given that you can eliminate at most k obstacles. If it is impossible to find such a path, return -1.

Given a root of a binary tree, return the maximum sum of all nodes in any BST (Binary Search Tree) subtree.

Given an m x n matrix mat where each row is sorted in non-decreasing order, and an integer k, return the k-th smallest sum among all possible arrays that you can form by choosing exactly one element from each row.

Given an m x n 2D binary grid which represents a map of '1's (land) and '0's (water), return the number of islands.

Given the root of a binary tree, return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Given a 2D matrix matrix, handle multiple queries of the following type: Calculate the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).

Given integers low, high, zero, and one. Return the number of 'good' strings, which are binary strings whose length is between low and high (inclusive) and contain zero consecutive '0's and one consecutive '1's.

You are given the root of a binary tree. We install cameras on some nodes of the tree. Each camera at a node can monitor itself, its parent, and its immediate children. Return the minimum number of cameras needed to monitor all nodes of the tree.

You are given a 0-indexed m x n grid of integers fire. You are in a cell (0, 0) and a fire starts at a cell (fireRow, fireCol). You want to reach a safe cell (m - 1, n - 1) before the fire reaches it. Return the maximum time t you can wait before starting your journey, such that you can still reach the safe cell. If it is impossible to ever reach the safe cell, return -1. If you can always reach the safe cell regardless of how long you wait, return 10^9.

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the i-th day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

Given an integer array nums, return the length of the longest strictly increasing subsequence.

You are given an m x n integer grid grid. You are also given an m x n integer matrix moveCost where moveCost[r][c] is the cost to move from a cell (r, c) to any cell in the next row column c'.

Implement a bank system with operations like transfer, deposit, and withdraw. This is a design problem often involving handling multiple accounts and transactions.

You are given an encoded string s and an integer k. To decode the string, this is how it works: if the character is a digit d, the encoded string is repeated d - 1 times. Return the k-th character of the decoded string.

You are given an array of distinct integers arr and an array of integer arrays pieces, where the integers in pieces are also distinct. Return true if arr can be formed by concatenating the arrays in pieces in any order.

A frog is trying to cross a river. The river is divided into some number of units, and at each unit, there may or may not be a stone. The frog can only jump on stones. Given a list of stone positions (in units) in sorted ascending order, determine if the frog can reach the last stone.

You have a 2-D grid of size m x n representing a box with some slanted walls. A ball will drop from the top of the box. The grid grid[i][j] can be 1 (representing a right-slanted wall) or -1 (representing a left-slanted wall). Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom, or -1 if it gets stuck.

You are given an integer N. In one move, you can either decrease N by 1 or decrease N to one of its divisors. Find the minimum number of moves to reach 0.

Given two strings str1 and str2 of the same length, determine whether you can transform str1 into str2 by doing zero or more conversions. In one conversion you can convert all occurrences of one character in str1 to any other lowercase English character.

Suppose LeetCode will start n projects for you. For each project i, you can choose to start it if you have at least capital[i] capital, and you'll earn profit[i] profit. You are given k projects to perform and your initial capital w. Maximize your final capital.

Design a search autocomplete feature. I used a Trie data structure and implemented a working solution. The discussion covered scalability, handling different scenarios, and optimization of memory and time complexity.

Design Instagram, focusing on core features like posting content, immediate post visibility, feed generation, and likes/comments. I covered non-functional requirements, set scale expectations, and outlined a high-level design, detailing each service and its trade-offs.

Design a service that registers triggers with specified delays from other services and sends a response once the delay for that trigger is completed.

Design an online multiplayer game like Ludo or Chess. I had to lead the discussion, covering functional and non-functional requirements, high-level design, APIs, tech stack choices, implementation details, exception handling, fault tolerance, and database choices. I also explained core logic for features like player matching (e.g., Noob vs. Noob) and presented multiple approaches with their trade-offs.

Design a system for payment gateway integration. The interviewers were looking for very specific details in the design.

Design Twitter, focusing on functionalities such as posting tweets, follow/following mechanisms, user timelines, and user profiles. The interview emphasized both Low-Level Design (LLD) and High-Level Design (HLD).

App Version Management System

• Install - Consumer just bought his / her first Mobile device and wants to use PhonePe. In such case a fresh Install will happen - always latest version supported will be installed. Consumer goes to phonepe website and selects install option given on website ( how it happens is outside the scope of problem statement )
• Update- Above customer has installed the app and a few days later a new feature ( say dark mode ) is rolled out by PhonePe. In such cases, PhonePe will directly update the app on the phone.

System Components -

• App and App versions - App will have a list of versions, each version denoting a new file and metadata. Version will have some meta data associated with it, like the minimum supported operating system ( android / iOS ) version etc.
• Roll out :: App admin can roll-out a new version from the backend. A roll-out can be either installing or updating the app -
  • install - App is to be installed fresh in the device. We will install the app in the smartphone
  • Update - takes a diff of installed version vs latest version and install the diff ( details in requirements part )
• Rollout strategy - New version rollout can be done with different strategies.
  • Beta rollout - roll out the app version only on specific devices
  • Percentage rollout - roll out the app version on some percent on devices

Requirements-

• Implement the above mentioned System components and their extensions (if possible)
• Implement the following functionalities for an app version management system. Note - We can use any of the available methods in the available capabilities section.

uploadNewVersion( // necessary params ) : Store the new version and version file byte stream in the system

createUpdatePatch( app, fromVersion, toVersion) : Create an update patch from source to target app version. Diff of fromVersion and toVersion will be a byte-stream or byte-array and same diff would be fired on the target device and pre-installed app will take care of installation. Pre Installed app has capability to accept a byte-stream / byte-array and install it as an update / patch

releaseVersion(// necessary params) : will release a version as per the strategy. BetaRolloutStartergy will include rolling out a new app version to only a set of devices.

isAppVersionSupported(// necessary params) : will check if given targetVersion supports the input device using info like like device android version, rollout strategies etc

checkForInstall(// necessary params) : Check whether a given h/w + OS supports the the app or not

checkForUpdates(// necessary params) : checks if an update is available for a given device.

executeTask(// necessary params) - will create an install or update task based on the method input. Can use methods from the list of available methods below.

Available Capabilities -

• installApp - will flash the app file in the device
• updateApp - will flash the diff pack in the device
• createDiffPack - will consume 2 app files and create diff pack file from sourceFile to targetFile
• uploadFile(fileContent) - will upload the file in some storage and return its url.
• getFile(fileUrl) - returns a file content, which could then be flashed using either installApp or updateApp methods

Code Expectations -

• Everything has to be in memory.
• Candidate can opt for any language for implementation
• Simple and basic function are expected as entry point - no marks for providing fancy restful API or framework implementation
• Because this is a machine coding round, try to at least complete the basic requirements with minimal required algorithm implementations.

Evaluation criteria -

• Working code
• Code readability
• Implementation of OOPs / OOD principles with proper Separation of concerns
• Testability - a TDD approach ( not to be mixed with test cases )
• Language proficiency
• Test Cases
• [execution time limit] 4 seconds (sh)
• [memory limit] 2g

For the machine coding round, I was given the complete problem statement for the classic Snake and Ladder game and had 24 hours to implement a solution.

In the DSA/Problem Solving round, one of the problems asked was similar to equalizing all elements in an array. This typically involves finding the minimum operations to make all elements the same, often related to finding a median or average.

For the system design round, I was asked to design a comprehensive Subscription Management System. This included aspects like handling recurring payments, managing different subscription plans, user upgrades/downgrades, cancellations, and notification systems.