Booking.com IOS Developer Interview Questions and Answers

Merge Sort is a divide and conquer algorithm that sorts an array by dividing it into two halves, sorting them separately, and then merging the sorted halves.

• Divide the array into two halves

• Recursively sort the two halves

• Merge the sorted halves

Find pairs of integers in a BST whose sum is equal to a given number.

• Traverse the BST and store the values in a hash set.

• For each node, check if (X - node.value) exists in the hash set.

• If yes, add the pair (node.value, X - node.value) to the result.

• Continue traversal until all nodes are processed.

Merge overlapping time intervals into mutually exclusive intervals.

• Sort the intervals based on their start time.

• Iterate through the intervals and merge overlapping intervals.

• Output the mutually exclusive intervals.

• Example: [(1,3), (2,6), (8,10), (15,18)] -> [(1,6), (8,10), (15,18)]

Different types of hashing and alternative for Linear Chaining

• Different types of hashing include division, multiplication, and universal hashing

• Alternative for Linear Chaining is Open Addressing

• Open Addressing includes Linear Probing, Quadratic Probing, and Double Hashing

An AVL tree is a self-balancing binary search tree where the heights of the left and right subtrees differ by at most one.

• AVL tree is a binary search tree with additional balance factor for each node.

• The balance factor is the difference between the heights of the left and right subtrees.

• Insertion and deletion operations in AVL tree maintain the balance factor to ensure the tree remains balanced.

• Rotations are performed ...read more

Find the minimum number of squares whose sum equals to a given number n.

• Use dynamic programming to solve the problem efficiently.

• Start with finding the square root of n and check if it is a perfect square.

• If not, then try to find the minimum number of squares required for the remaining number.

• Repeat the process until the remaining number becomes 0.

• Return the minimum number of squares required for the given number n.

Insertion sort for a singly linked list.

• Traverse the list and compare each node with the previous nodes

• If the current node is smaller, swap it with the previous node

• Repeat until the end of the list is reached

• Time complexity is O(n^2)

Reverse a binary search tree while maintaining parent-child relationship.

• Start by swapping the left and right child of each node recursively.

• Use a depth-first search approach to traverse the tree.

• Make sure to update the parent-child relationships accordingly.

To find min and max element in stack in O(1), we can use an auxiliary stack.

• Create an auxiliary stack to keep track of the minimum and maximum elements.

• Push the first element to both the main and auxiliary stack.

• For each subsequent element, compare it with the top element of the auxiliary stack and push the smaller element to the auxiliary stack.

• To get the minimum element, simply return the top element of the auxiliary...read more

Given an array, find the next minimum element for each element.

• Iterate through the array

• For each element, compare it with the elements on its right

• Find the minimum element greater than the current element

• If no such element exists, assign -1

• Build the resultant array

Find median of input stream in minimum time complexity using online algorithm.

• Use two heaps, one max heap for elements smaller than current median and one min heap for elements greater than current median.

• Maintain balance between the two heaps by ensuring that the size difference is at most 1.

• If the size of both heaps is equal, median is the average of the top elements of both heaps. Else, median is the top element of ...read more

To make a copy of a linked list with two pointers, iterate through the original list and create a new node for each element.

• Iterate through the original linked list

• Create a new node for each element

• Set the 'next' pointer of each new node

• Set the 'arbitrary' pointer of each new node

Reverse the nodes of a linked list in pairs of n

• Iterate through the linked list in pairs of n

• Reverse the nodes within each pair

• Connect the reversed pairs together

• Handle cases where the number of nodes is not a multiple of n

To check if a singly linked list is a palindrome, reverse the second half and compare it with the first half.

• Traverse the linked list to find the middle node

• Reverse the second half of the linked list

• Compare the reversed second half with the first half to check for palindrome

Given a preorder of binary tree with leaf nodes represented by N, construct the tree.

• Start by creating an empty stack.

• Iterate through the preorder list.

• If the current element is N, create a leaf node and push it onto the stack.

• If the current element is not N, create a new node and set its left child to the top of the stack.

• Pop the top of the stack and set it as the right child of the new node.

• Push the new node onto the...read more

The question asks to find the maximum occupancy word in each line of a given multiline string and also count the occupancy of capital and small letters separately.

• Split the multiline string into individual lines

• For each line, split it into words

• Initialize variables to store the maximum occupancy word and its count

• Iterate through each word and count the occupancy of each letter

• If the current word has a higher occupancy ...read more

Algorithm to find the best buying and selling dates for maximum profit from given stock prices array.

• Iterate through the array and keep track of minimum price and maximum profit.

• If current price is less than minimum price, update minimum price.

• If current price minus minimum price is greater than maximum profit, update maximum profit and buying and selling dates.

• Return buying and selling dates.

• Example: [10, 7, 5, 8, 11,...read more

The code finds the number of ways to reach n steps by jumping 1 or 2 steps at a time.

• Use dynamic programming to solve the problem

• Create an array to store the number of ways to reach each step

• Initialize the array with base cases for 0 and 1 steps

• Iterate through the array and calculate the number of ways for each step

• Return the value at the last step

Amazon.com is an online retail giant with a vast selection of products and services.

• Advantages: Wide selection of products, competitive pricing, fast shipping, convenient shopping experience

• Disadvantages: Can put smaller retailers out of business, concerns over worker treatment and environmental impact

• Example: Amazon Prime offers free two-day shipping and access to streaming services like Prime Video and Music

• Example: ...read more

Use file locking mechanisms like flock or lockfile to make a file mutually exclusive on a shared file system.

• Use flock or lockfile to acquire a lock on the file before accessing it.

• Release the lock once the operation is complete.

• Ensure all processes accessing the file use the same locking mechanism.

• Example: flock /path/to/file -c 'command to execute'

• Example: lockfile /path/to/file && command to execute && rm -f /path/t

I am a software developer with 5 years of experience in developing web applications using Java and JavaScript.

• 5 years of experience in software development

• Proficient in Java and JavaScript

• Developed web applications

• Strong problem-solving skills

• Experience with agile development methodologies

Positive: Strong problem-solving skills, Negative: Can be overly critical of own work

• Positive: Strong problem-solving skills - I excel at breaking down complex problems and finding efficient solutions

• Negative: Can be overly critical of own work - I tend to be perfectionistic and struggle with accepting imperfections

I had a failure in implementing a new feature due to a lack of understanding of the requirements.

• I was assigned to develop a new feature for our software application.

• I misunderstood the requirements and implemented the feature incorrectly.

• During the testing phase, it was discovered that the feature was not functioning as expected.

• I took responsibility for the mistake and immediately communicated it to my team lead.

• I wo...read more

Replace every element in array with its closest maximum element in right.

• Iterate through the array from right to left

• Keep track of the maximum element seen so far

• Replace each element with the maximum element seen so far

Designing a distributed Hashtable and discussing its pros and cons.

• Distributed Hashtable is a data structure that stores key-value pairs across multiple nodes.

• Pros include scalability, fault tolerance, and load balancing.

• Cons include increased complexity, potential for data inconsistency, and slower performance due to network communication.

• Examples of distributed Hashtable implementations include Cassandra, Riak, and D

To identify if a tree is a BST, check if the inorder traversal of the tree results in a sorted sequence.

• Perform an inorder traversal of the tree

• Check if the resulting sequence is sorted in ascending order

• If yes, the tree is a BST; otherwise, it is not

My favorite subject is computer science and I excel in problem-solving and algorithm design.

• Computer science is my favorite subject because I enjoy coding and creating software applications.

• I am best at problem-solving, as I have a strong analytical mindset and can efficiently break down complex issues.

• I excel in algorithm design, as I have a deep understanding of data structures and can optimize code for efficiency.

Paging is a memory management technique used by operating systems to manage memory more efficiently. Virtual memory is a technique that allows a computer to use more memory than it physically has available.

• Paging divides memory into fixed-size blocks called pages.

• Virtual memory allows programs to use more memory than is physically available by temporarily transferring pages of data from RAM to disk.

• Virtual memory also ...read more

The remaining memory is not wasted, but reserved for other system processes and applications.

• The operating system reserves a portion of the RAM for its own processes and functions.

• The unused memory can be used for caching data, improving system performance.

• Applications and processes may not require the full amount of RAM at all times.

• The unused memory can be allocated to other applications when needed.

• Virtual memory an...read more

Return the total possible positions for a knight on a chess board given the number of combinations of moves.

• Calculate all possible positions for a knight on a chess board using its unique L-shaped moves.

• Consider the boundaries of the chess board while calculating the positions.

• The total possible positions for a knight on a chess board are 64.

Use file locking mechanism to ensure mutual exclusion.

• Implement file locking mechanism to prevent simultaneous access to files.

• Use semaphores or mutexes to ensure only one process can access a file at a time.

• Implement a queue system to handle multiple requests and process them one by one.

• Use transactional file systems to ensure atomicity of file operations.

• Implement a timeout mechanism to prevent deadlocks.

• Consider imp...read more

Implementing a hash table in code

• Choose a hash function to map keys to indices in the table

• Create an array to hold the values at each index

• Handle collisions by using a collision resolution strategy

• Implement methods for inserting, retrieving, and deleting values

• Consider load factor and resizing the table if necessary

The given question asks to replace the value in each node of a binary search tree with the sum of all nodes greater than the current node.

• Traverse the BST in reverse order (right, root, left)

• Keep track of the sum of all greater nodes encountered so far

• Update the value of each node with the sum and update the sum

The next inorder predecessor in a binary search tree (BST) is the node with the largest value smaller than the given node.

• In a BST, the inorder predecessor of a node is the rightmost node in its left subtree.

• If the left subtree of the given node is empty, then the inorder predecessor is the nearest ancestor whose right child is also an ancestor of the given node.

• If there is no inorder predecessor (i.e., the given node

Generate all possible parentheses for a given integer n.

• Use recursion to generate all possible combinations of parentheses.

• Start with an empty string and keep adding opening and closing parentheses.

• Keep track of the number of opening and closing parentheses used.

• Stop recursion when the number of opening and closing parentheses reaches n.

• Add the generated combination to the result array.

The question asks how to feed a 2D matrix with values based on the given binary tree.

• Traverse the binary tree and for each node, update the corresponding row in the matrix

• Use a recursive function to update the matrix values

• Start with the root node and recursively update its descendants

• Set M[i, j] to 1 if node i is an ancestor of node j

• Repeat the process for all nodes in the binary tree

Find the first occurrence of a given key element in a sorted array with duplicates.

• Use binary search to find the key element.

• If the key element is found, check if it is the first occurrence by checking the previous element.

• If the key element is not found, return -1.

Spiral order traversal of a binary tree

• Use a stack and a queue to traverse the binary tree in a spiral order

• Start with the root node and add it to the stack

• While the stack is not empty, pop a node from the stack and add its children to the queue

• If the stack is empty, swap the stack and queue

• Repeat until both stack and queue are empty

Queue can be implemented using two stacks by maintaining the order of elements.

• Use two stacks, one for enqueue operation and one for dequeue operation

• When enqueue is called, push the element onto the enqueue stack

• When dequeue is called, if the dequeue stack is empty, transfer all elements from enqueue stack to dequeue stack

• Pop the top element from the dequeue stack and return it as the dequeued element

Edit distance problem is a dynamic programming problem to find the minimum number of operations required to transform one string into another.

• The problem can be solved using dynamic programming approach

• The solution involves filling up a matrix of size (m+1)x(n+1)

• The matrix represents the minimum number of operations required to transform one string into another

• The operations include insertion, deletion and substitution

• ...read more

To find a loop in a linked list, we can use the Floyd's cycle-finding algorithm.

• Initialize two pointers, slow and fast, both pointing to the head of the linked list.

• Move slow pointer by one step and fast pointer by two steps at each iteration.

• If there is a loop, the slow and fast pointers will eventually meet.

• To prove the algorithm, we can use mathematical induction and the concept of tortoise and hare.