Koo App Senior Android Developer Interview Questions and Answers

Q1. Explain hoisting in js
Ans. 
Hoisting in JavaScript is the behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase.
• Variable declarations are hoisted to the top of their scope, but not their assignments.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

• Hoisting can lead to unexpected behavior if not understood properly.
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Q2. Explain closures in js
Ans. 
Closures in JavaScript allow functions to access variables from their outer scope even after the outer function has finished executing.
• Closures are created when a function is defined within another function and the inner function has access to the outer function's variables.

• Closures can be used to create private variables and functions in JavaScript.

• Closures can also be used to maintain state in asynchronous operations...read more
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Q1. Javascript polyfills
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Round duration - 60 Minutes
Round difficulty - Easy

Formal Introduction.
Asked About Projects.
Difference between SQL and NoSQL. Pros and Cons. Where should we use SQL and NoSQL.
Given a problem, I have to make a SQL Database structure and then interviewer told me to convert it into NoSQL.
asked coding questions

Q1. 
Search In Rotated Sorted Array Problem Statement
Given a sorted array of distinct integers that has been rotated clockwise by an unknown amount, you need to search for a specified integer in the array. Fo...read more
Ans. 
Implement a search function to find a specified integer in a rotated sorted array.
• Implement a binary search algorithm to find the target integer in the rotated sorted array.

• Handle the cases where the target integer may lie in the left or right half of the rotation.

• Keep track of the mid element and adjust the search range based on the rotation.

• Return the index of the target integer if found, else return -1.
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Q2. 
Zigzag Binary Tree Traversal Problem
Given a binary tree, compute the zigzag level order traversal of the node values in the tree. The zigzag traversal requires traversing levels from left to right, then ...read more
Ans. 
Zigzag level order traversal of a binary tree is computed by alternating between left to right and right to left traversal at each level.
• Use a queue to perform level order traversal of the binary tree.

• Maintain a flag to switch between left to right and right to left traversal at each level.

• Store the node values in a list while traversing and alternate the order based on the flag.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -...read more
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Computer Fundamentals

Q1. Flatten a binary tree
Ans. 
Flatten a binary tree by converting it into a linked list in-place.
• Use a recursive approach to flatten the binary tree.

• Traverse the tree in a pre-order manner and keep track of the previous node.

• Set the left child of each node to null and the right child to the next node in the linked list.

• Example: Input: 1 -> 2 -> 5 -> 3 -> 4 -> null, Output: 1 -> null -> 2 -> null -> 3 -> null -> 4 -> null -> 5 -> null
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Q1. Class vs struct
Ans. 
Classes are reference types; structs are value types. Classes support inheritance, while structs are more lightweight and efficient.
• Classes support inheritance, allowing for polymorphism.

• Structs are value types, meaning they are copied on assignment.

• Classes are reference types, meaning they are accessed via references.

• Structs are generally more memory efficient for small data structures.

• Example: class Person { string N...read more
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Q2. Thread question
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Round duration - 90 minutes
Round difficulty - Hard

Timing was late evening . Platform was good.

Q1. 
Largest Cycle in Maze Problem Statement
Given a maze represented by 'N' cells numbered from 0 to N-1, and an array arr of 'N' integers where arr[i] denotes the cell number that can be reached from the 'i'...read more
Ans. 
Identify the length of the largest cycle in a maze represented by cells and an array of integers.
• Iterate through each cell and find the cycle length using DFS or Floyd's Tortoise and Hare algorithm.

• Keep track of visited cells to avoid infinite loops.

• Return the length of the largest cycle found or -1 if no cycles exist.
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Round duration - 90 minutes
Round difficulty - Medium

The coding round was 90 minutes with 2 question and the difficulty was mid-range and both were graph question

Q1. 
Rat in a Maze Problem Statement
You need to determine all possible paths for a rat starting at position (0, 0) in a square maze to reach its destination at (N-1, N-1). The maze is represented as an N*N ma...read more
Ans. 
Find all possible paths for a rat in a maze from start to destination.
• Use backtracking to explore all possible paths in the maze.

• Keep track of visited cells to avoid revisiting them.

• Explore all possible directions (up, down, left, right) from each cell.

• Add the current direction to the path and recursively explore further.

• When reaching the destination, add the path to the list of valid paths.
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3 Graph Questions Were asked of difficulty medium to hard.

Hackathon round which revolved around multithreading

They have their own coding platform. The questions are basically from tree.

Tree of space question

Q1. Previous round question solution
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Q2. System design was asked.
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