60+ Lexspectrum Interview Questions and Answers

Find the most repeated number in an array of length n with numbers 1-n.

• Create a dictionary to store the count of each number in the array

• Iterate through the array and update the count in the dictionary

• Find the key with the highest count in the dictionary

Find the triplicate number in an array of duplicates.

• Iterate through the array and keep track of the frequency of each number.

• Return the number that appears three times.

• If no number appears three times, return null.

Reverse m nodes and leave n nodes in a linked list till the end.

• Traverse the linked list till m nodes and reverse them

• Traverse n nodes and continue reversing m nodes

• Repeat the above step till the end of the linked list

• Handle edge cases like m or n being greater than the length of the linked list

Print only the leaf nodes of a doubly linked tree.

• Traverse the tree and check if a node has no children and both left and right pointers are null.

• If yes, then it is a leaf node and print it.

• If no, then continue traversing the tree.

• Use recursion to traverse the tree in a depth-first manner.

Session ID is stored in PHP as a cookie or a query parameter.

• Session ID can be stored as a cookie in the client's browser.

• Session ID can also be stored as a query parameter in the URL.

• The server identifies the client by retrieving the session ID from the cookie or query parameter.

• The session ID is then used to retrieve the corresponding session data stored on the server.

• The server can also use other methods like IP address or user agent to identify the client.

Rearrange an array of positive and negative numbers with positive numbers on the left and negative numbers on the right.

• Create two empty arrays, one for positive numbers and one for negative numbers

• Loop through the original array and add positive numbers to the positive array and negative numbers to the negative array

• Concatenate the positive and negative arrays to create the rearranged array

String pool is a cache of string literals in memory. Garbage collection frees up memory by removing unused objects.

• String pool is a cache of string literals in memory

• Strings are immutable and can be shared among multiple objects

• Garbage collection removes unused objects to free up memory

• String objects that are no longer referenced are eligible for garbage collection

The question asks to find two elements in an array whose sum is equal to a given number.

• Iterate through the array and for each element, check if the difference between the given number and the current element exists in the array.

• Use a hash set to store the elements as you iterate through the array for efficient lookup.

• Return the pair of elements if found, otherwise return a message indicating no such pair exists.

Change binary tree to make parent node the sum of root nodes

• Traverse the tree in post-order

• For each node, update its value to the sum of its children

• Return the updated root node

Yes

• Create an empty binary search tree (BST)

• Loop over the unsorted array

• For each element, insert it into the BST using the appropriate insertion logic

• Repeat until all elements are inserted

• The resulting BST will be built from the unsorted array

Explanation of search algorithms with their space and time complexities.

• Linear Search - O(n) time complexity, O(1) space complexity

• Binary Search - O(log n) time complexity, O(1) space complexity

• Jump Search - O(√n) time complexity, O(1) space complexity

• Interpolation Search - O(log log n) time complexity, O(1) space complexity

• Exponential Search - O(log n) time complexity, O(1) space complexity

• Fibonacci Search - O(log n) time complexity, O(1) space complexity

Inorder traversal of a tree without recursion

• Create an empty stack and initialize current node as root

• Push the current node to stack and set current = current.left until current is NULL

• If current is NULL and stack is not empty, pop the top item from stack, print it and set current = popped_item.right

• Repeat step 2 and 3 until stack is empty

Indexing in MySQL improves query performance. There are several types of indexing in MySQL.

• Indexes are used to quickly locate data without scanning the entire table.

• Types of indexing in MySQL include B-tree, hash, full-text, and spatial indexes.

• B-tree indexes are the most common and suitable for most use cases.

• Hash indexes are used for exact match lookups.

• Full-text indexes are used for searching text-based data efficiently.

• Spatial indexes are used for optimizing spatial queri...read more

GET is used to retrieve data from a server, while POST is used to send data to a server.

• GET requests are idempotent, meaning they can be repeated without changing the result

• POST requests are not idempotent and can have side effects on the server

• GET requests can be cached by the browser, while POST requests cannot

• GET requests have limitations on the amount of data that can be sent, while POST requests have no limitations

• GET requests should not be used for sensitive data, as th...read more

Process vs Thread differences and synchronization, deadlock examples

• Process is an instance of a program while thread is a subset of a process

• Processes are independent while threads share the same memory space

• Synchronization is used to coordinate access to shared resources

• Deadlock occurs when two or more threads are blocked waiting for each other to release resources

• Examples of synchronization include mutex, semaphore, and monitor

• Examples of deadlock include dining philosopher...read more

Yes, triggers can be used with select statements in SQL.

• Triggers are database objects that are automatically executed in response to certain events, such as insert, update, or delete operations.

• While triggers are commonly used with insert, update, and delete statements, they can also be used with select statements.

• Using triggers with select statements allows you to perform additional actions or validations before or after the select operation.

• For example, you can use a trigge...read more

LRU page replacement algorithm is used to replace the least recently used page in memory with a new page.

• LRU stands for Least Recently Used

• It is a cache eviction algorithm

• It is used to manage memory in operating systems

• It works by keeping track of the pages that are used recently and the ones that are not

• When a new page is to be loaded into memory, the algorithm checks which page has not been used for the longest time and replaces it with the new page

Yes, a constructor can be declared as private.

• Declaring a constructor as private restricts its accessibility to only the class itself.

• This can be useful in scenarios where you want to control the creation of objects of that class.

• Private constructors are commonly used in singleton design pattern implementations.

• Example: private constructor in a singleton class:

• class Singleton { private Singleton() {} }

Use stack to keep track of indices of opening parentheses, update max length when closing parentheses found

• Use a stack to keep track of indices of opening parentheses

• When a closing parentheses is found, update max length by calculating the difference between current index and top of stack

• Handle edge cases like extra closing parentheses or unmatched opening parentheses

• Example: Input: "(()()", Output: 4 (for "()()")

A cookie in PHP is a small piece of data stored on the client's computer. It has a size limit and an expiry date.

• A cookie is used to store information on the client's computer for future use.

• In PHP, cookies are set using the setcookie() function.

• The size of a cookie is limited to 4KB.

• Cookies can have an expiry date, after which they are no longer valid.

• The expiry date can be set using the 'expires' parameter in the setcookie() function.

• If no expiry date is set, the cookie wil...read more

Find the longest palindromic substring in a given string.

• Use dynamic programming to check for palindromes within the string.

• Start by checking for palindromes of length 1 and 2, then expand to longer substrings.

• Keep track of the longest palindrome found so far.

Yes, a constructor can be private.

• A private constructor can only be accessed within the class itself.

• It is often used in singleton design pattern to restrict object creation.

• Private constructors are also useful for utility classes that only contain static methods.

Session in PHP is a way to store and retrieve data for a user across multiple requests.

• Sessions are used to maintain user-specific data on the server side.

• A session is created for each user and is identified by a unique session ID.

• Session data can be stored in server files or in a database.

• Session variables can be accessed and modified throughout the user's session.

• Sessions can be used to implement features like user authentication and shopping carts.

There are two types of triggers: DML triggers and DDL triggers.

• DML triggers are fired in response to DML (Data Manipulation Language) statements like INSERT, UPDATE, DELETE.

• DDL triggers are fired in response to DDL (Data Definition Language) statements like CREATE, ALTER, DROP.

• Examples: A DML trigger can be used to log changes made to a table, while a DDL trigger can be used to enforce certain rules when a table is altered.

Inorder traversal is a way of visiting all nodes in a binary tree by visiting the left subtree, then the root, and then the right subtree.

• Start at the root node

• Traverse the left subtree recursively

• Visit the root node

• Traverse the right subtree recursively

• Repeat until all nodes have been visited

PreOrder traversal without recursion is done using a stack to simulate the function call stack.

• Create an empty stack and push the root node onto it.

• While the stack is not empty, pop a node from the stack and process it.

• Push the right child of the popped node onto the stack if it exists.

• Push the left child of the popped node onto the stack if it exists.

Reverse a linkedlist by changing the direction of pointers.

• Iterate through the linkedlist and change the direction of pointers.

• Keep track of previous, current and next nodes.

• Set the next pointer of current node to previous node.

• Move to next node and repeat until end of list is reached.

A linked list can be implemented in a binary tree by using the left child as the next node and the right child as the previous node.

• Each node in the binary tree will have a left child pointer and a right child pointer.

• Traversal of the linked list can be done by following the left child pointers.

• Example: In a binary tree, the left child of a node can point to the next node in the linked list.

3 sum and trapping rain water are common coding interview questions that test problem-solving skills.

• 3 sum problem involves finding three numbers in an array that add up to a target sum.

• Trapping rain water problem involves calculating the amount of water that can be trapped between bars in an elevation map.

• Both problems require efficient algorithms to solve.

Engines in MySQL are the underlying software components that handle storage, indexing, and querying of data.

• MySQL supports multiple storage engines, each with its own strengths and features.

• Some commonly used engines in MySQL are InnoDB, MyISAM, and Memory.

• InnoDB is the default engine in MySQL and provides support for transactions and foreign keys.

• MyISAM is known for its simplicity and speed but lacks transaction support.

• Memory engine stores data in memory for faster access b...read more

Triggers in MySQL are database objects that are automatically executed in response to specified events.

• Triggers are used to enforce business rules, maintain data integrity, and automate tasks.

• They can be defined to execute before or after an INSERT, UPDATE, or DELETE operation.

• Triggers can be written in SQL or in a programming language like PL/SQL.

• Examples of trigger events include inserting a new record, updating a record, or deleting a record.

• Triggers can be used to perform...read more

Indexing in MySQL improves the performance of database queries by creating a data structure that allows for faster data retrieval.

• Indexes are created on one or more columns of a table.

• They help in speeding up the search, sorting, and joining of data.

• Indexes can be created using the CREATE INDEX statement.

• Common types of indexes include B-tree, hash, and full-text indexes.

• Indexes should be used judiciously as they consume disk space and require additional maintenance.

LRU cache is a data structure that stores the most recently used items, discarding the least recently used items when full.

• Use a combination of a doubly linked list and a hashmap to efficiently implement LRU cache.

• When an item is accessed, move it to the front of the linked list to mark it as the most recently used.

• When adding a new item, check if the cache is full. If so, remove the least recently used item from the end of the linked list and hashmap.

• Keep track of the size o...read more