Hopscotch Backend Developer Interview Questions and Answers

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.

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

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.

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 alt

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 af...read more

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 efficie...read more

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 suppo...read more

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.