10+ Junior Backend Developer Interview Questions and Answers

Trees are a type of graph with a hierarchical structure. Graphs are a collection of nodes and edges.

• Trees have a single root node, while graphs can have multiple disconnected nodes.

• Traversal of trees can be done using depth-first or breadth-first search algorithms.

• Traversal of graphs can be done using various algorithms like Dijkstra's algorithm, Bellman-Ford algorithm, etc.

The UPDATE query is used to modify existing data in a database table.

• The UPDATE query is followed by the name of the table and the SET keyword to specify the columns to be updated.

• The WHERE clause is used to specify the condition for updating specific rows.

• Multiple columns can be updated in a single UPDATE query.

• The UPDATE query can be used with various operators like =, +, -, *, /, etc.

• Example: UPDATE employees SET salary = 50000 WHERE department = 'IT';

Invert a given binary tree by swapping left and right child nodes recursively.

• Recursively swap left and right child nodes of each node in the binary tree.

• Start from the root node and swap its left and right child nodes.

• Then, recursively swap the left and right child nodes of the left and right child nodes of the root node.

• Repeat the process until all nodes have been swapped.

• Return the inverted binary tree.

Use the 'kill' command followed by the process ID to terminate a process in Linux.

• Use 'ps' command to find the process ID of the process you want to kill

• Use 'kill' command followed by the process ID to terminate the process

• You can also use 'kill -9' followed by the process ID for a forceful termination

JWT (JSON Web Token) is a compact, URL-safe means of representing claims to be transferred between two parties.

• JWT consists of three parts: header, payload, and signature.

• Header typically consists of the type of token and the signing algorithm being used.

• Payload contains the claims. Claims are statements about an entity (typically the user) and additional data.

• Signature is created by encoding the header, payload, a secret, and the algorithm specified in the header.

• JWTs are ty...read more

LinkedList is a data structure where each element points to the next element, while ArrayList is a resizable array implementation.

• LinkedList uses pointers to connect elements, while ArrayList uses an underlying array to store elements.

• LinkedList allows for efficient insertion and deletion of elements, while ArrayList is more efficient for random access.

• LinkedList is not contiguous in memory, while ArrayList is contiguous in memory.

• Example: LinkedList: 1 -> 2 -> 3 -> 4, ArrayL...read more

CORS is used to allow or restrict cross-origin requests in web applications.

• CORS is used to prevent malicious websites from making unauthorized requests to a different origin.

• It allows servers to specify who can access their resources by setting appropriate headers.

• CORS is important for security and privacy reasons in web development.

• Example: If a frontend application on domain A wants to make a request to a backend API on domain B, CORS must be implemented to allow this comm...read more

Code for sorting an array of strings

• Use a sorting algorithm like bubble sort, selection sort, or quicksort

• Implement the sorting algorithm in a function that takes an array of strings as input

• Return the sorted array of strings

The Target Sum problem involves finding ways to assign '+' or '-' to numbers to reach a specific target sum.

• Dynamic Programming (DP) approach is used to solve this problem efficiently.

• Example: Given numbers [1, 1, 2, 3] and target sum 1, possible combinations are: +1 -1 +2 -3.

• Create a DP table to store results of subproblems, reducing redundant calculations.

• Base case: If the target is 0, there's one way to achieve it (by not selecting any number).

• The problem can be transforme...read more