Apple Interview Questions

Intermediate Level Apple Interview Questions and Answers

11. Describe the process of a TCP handshake.

A TCP handshake is a three-step process that establishes a reliable connection between a client and a server. The steps are as follows:

• SYN: The client sends a SYN (synchronize) packet to the server, specifying the initial sequence number.
• SYN-ACK: The server responds with a SYN-ACK packet, acknowledging the client's SYN and specifying its own initial sequence number.
• ACK: The client sends an ACK (acknowledgment) packet to the server, acknowledging the server's SYN-ACK.

After these three steps, a reliable connection is established, and data can be transmitted between the client and the server.

12. Explain the ACID properties in databases.

ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure the reliability and integrity of database transactions

• Atomicity: A transaction is an indivisible unit of work. It either completes entirely or not at all, even in the event of failures.
• Consistency: A transaction must bring the database from one valid state to another, maintaining data integrity and consistency.
• Isolation: Concurrent transactions must be isolated from each other, preventing interference and ensuring that the result is as if the transactions were executed sequentially.
• Durability: Once a transaction is committed, its effects must persist permanently, even in the case of system failures.

13. Find the longest substring without repeating characters in a given string.

def length_of_longest_substring(s):
    char_set = set()
    max_length = 0
    left = right = 0
    
    while right < len(s):
        if s[right] not in char_set:
            char_set.add(s[right])
            max_length = max(max_length, right - left + 1)
            right += 1
        else:
            char_set.remove(s[left])
            left += 1
    
    return max_length

You can also try this code with Online Python Compiler

Run Code

14. Explain the difference between IPv4 and IPv6.

15. Implement a queue using two stacks. 

Here's a Python code example to implement a queue using two stacks:

class Queue:
    def __init__(self):
        self.stack1 = []
        self.stack2 = []
    
    def enqueue(self, element):
        self.stack1.append(element)
    
    def dequeue(self):
        if not self.stack2:
            while self.stack1:
                self.stack2.append(self.stack1.pop())
        
        if not self.stack2:
            raise IndexError("Queue is empty")
        
        return self.stack2.pop()
    
    def front(self):
        if not self.stack2:
            while self.stack1:
                self.stack2.append(self.stack1.pop())
        
        if not self.stack2:
            raise IndexError("Queue is empty")
        
        return self.stack2[-1]
    
    def is_empty(self):
        return len(self.stack1) == 0 and len(self.stack2) == 0

You can also try this code with Online Python Compiler

Run Code

16. How does NAT (Network Address Translation) work?

NAT is a technique used to allow multiple devices on a private network to share a single public IP address. It works by modifying the source IP address and port number of outgoing packets and the destination IP address and port number of incoming packets. The process is as follows:

1. When a device on the private network sends a packet to the internet, NAT replaces the device's private IP address with the public IP address of the NAT device.
2. NAT also replaces the source port number with a unique port number from a pool of available ports.
3. NAT maintains a translation table that maps the private IP address and port number to the public IP address and assigned port number.
4. When a response packet arrives from the internet, NAT uses the translation table to determine the original private IP address and port number.
5. NAT replaces the destination IP address and port number with the corresponding private IP address and port number and forwards the packet to the appropriate device on the private network.
6. NAT provides several benefits, such as conserving public IP addresses, enhancing security by hiding the internal network structure, and enabling multiple devices to share a single internet connection.

17. What is an index, and how does it improve query performance?

An index is a data structure in a database that improves the speed of data retrieval operations on a table. It allows the database to quickly locate and access specific rows based on the indexed columns without scanning the entire table. Here's how an index improves query performance:

• Faster data retrieval: An index acts as a pointer to the location of data, enabling quick lookups and reducing the need for full table scans.
• Efficient sorting: Indexes store data in a sorted order, making it faster to retrieve data in a specific order without sorting the entire table.
• Improved join performance: Indexes on foreign key columns can speed up join operations by quickly locating matching rows in related tables.
• Reduced I/O operations: By using indexes, the database can read fewer data pages from disk, minimizing I/O operations and improving overall performance.

18. Implement a function to merge two sorted linked lists.

Here's a Python code example to merge two sorted linked lists:

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def merge_two_lists(l1, l2):
    dummy = ListNode()
    p = dummy
    
    while l1 and l2:
        if l1.val <= l2.val:
            p.next = l1
            l1 = l1.next
        else:
            p.next = l2
            l2 = l2.next
        p = p.next
    
    if l1:
        p.next = l1
    if l2:
        p.next = l2
    
    return dummy.next

You can also try this code with Online Python Compiler

Run Code

19. How do you optimize SQL queries?

To optimize SQL queries and improve database performance, you can follow these techniques:

• Use appropriate indexes: Create indexes on columns frequently used in WHERE clauses, JOIN conditions, and ORDER BY clauses to speed up data retrieval.
• Avoid SELECT *: Specify only the required columns in the SELECT statement to reduce the amount of data transferred and improve query performance.
• Use JOIN instead of subqueries: Whenever possible, use JOIN operations instead of correlated subqueries as they are generally more efficient.
• Use EXPLAIN: Utilize the EXPLAIN command to analyze the query execution plan and identify performance bottlenecks.
• Optimize database configuration: Tune database parameters such as buffer sizes, caches, and memory allocation to match the workload and available resources.
• Regularly update statistics: Keep the database statistics up to date to ensure the query optimizer makes informed decisions based on accurate data distribution.

20. What are the security features in modern operating systems?

Modern operating systems incorporate several security features to protect against unauthorized access, malware, and other security threats. Some of the key security features are:

• User authentication: Operating systems require users to authenticate themselves using passwords, biometric data, or other methods to ensure only authorized users can access the system.
• Access control: Operating systems implement access control mechanisms, such as file permissions and user roles, to restrict access to system resources based on user privileges.
• Encryption: Encryption techniques are used to protect sensitive data both at rest and in transit, ensuring confidentiality and integrity.
• Data execution prevention (DEP): DEP marks certain memory regions as non-executable, preventing the execution of malicious code injected into those regions.
• Firewalls: Built-in firewalls monitor and control network traffic, blocking unauthorized access and protecting against network-based attacks.
• Regular updates and patches: Operating systems provide regular security updates and patches to fix vulnerabilities and protect against newly discovered threats.
• Antivirus and anti-malware: Many operating systems include or support antivirus and anti-malware software to detect and remove malicious software.

Advanced Level Apple Interview Questions and Answers

21.Describe QoS (Quality of Service) and how it is implemented in networking.

Quality of Service (QoS) refers to the ability of a network to provide different priorities to different applications, users, or data flows, ensuring a certain level of performance. QoS is implemented through various techniques:

1. Classification: Network traffic is classified based on criteria such as IP address, port number, or application type.
2. Marking: Packets are marked with a specific QoS label or priority level.
3. Queuing: Different queues are used to handle packets with different priorities. High-priority packets are sent first.
4. Scheduling: Scheduling algorithms, such as Weighted Fair Queuing (WFQ) or Priority Queuing (PQ), determine the order in which packets are sent.
5. Policing and Shaping: These mechanisms limit the bandwidth used by certain traffic flows to prevent network congestion.

QoS ensures that critical applications or services receive the necessary network resources and performance, even during network congestion.

22. Explain the different types of file systems (e.g., NTFS, FAT32, ext4) and their features.

23. Implement a depth-first search (DFS) algorithm for a graph. 

def dfs(graph, start, visited=None):
    if visited is None:
        visited = set()
    visited.add(start)
    print(start)
    for neighbor in graph[start]:
        if neighbor not in visited:
            dfs(graph, neighbor, visited)

# Example usage
graph = {
    'A': ['B', 'C'],
    'B': ['A', 'D', 'E'],
    'C': ['A', 'F'],
    'D': ['B'],
    'E': ['B', 'F'],
    'F': ['C', 'E']
}

dfs(graph, 'A')

You can also try this code with Online Python Compiler

Run Code

24. How do VPNs (Virtual Private Networks) work and what are their benefits?

VPNs create a secure, encrypted tunnel between a device and a remote network over the internet. They work by encapsulating and encrypting the data packets sent between the device and the VPN server. 

Benefits of VPNs are:

• Secure remote access to private networks
• Encrypted communication to protect sensitive data
• Anonymity and privacy by masking the user's IP address
• Bypassing geographical restrictions and censorship
• Protection against public Wi-Fi security threats

25. In which cases, can we use a stored procedure?

Stored procedures can be used in the following situations:

1. Encapsulate large and complex database operations: A stored procedure can bundle up multiple instructions into a single callable unit. This simplifies the code we are working on & ensures consistency.
2. Improves performance: Since stored procedures are precompiled & stored on the database server, they can execute faster than individual SQL statements sent though a client. They also helps in reducing network traffic.
3. Enhances security: Stored procedures can be used to control access to the underlying tables. Permission can be granted to users to execute a procedure without a direct access to the tables.

26. Write a program to detect a cycle in a linked list. 

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def has_cycle(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        if slow == fast:
            return True
    return False

You can also try this code with Online Python Compiler

Run Code

27. How does the operating system handle context switching?

Context switching is the process of saving the state of a currently executing process or thread and restoring the state of another process or thread to resume its execution. The operating system performs context switching through the following steps:

1. Save the current process's state (registers, program counter, stack pointer) in its Process Control Block (PCB).
2. Update the PCB of the current process with its new state (e.g., running, ready, waiting).
3. Select the next process to be executed based on the scheduling algorithm.
4. Load the state of the selected process from its PCB into the CPU registers.
5. Update the memory management structures to reflect the new process's memory mappings.
6. Resume the execution of the selected process from where it left off.
7. Context switching allows multiple processes to share the CPU time and enables multitasking in operating systems.

28. Describe the process of routing in a network.

Routing is the process of forwarding data packets from the source to the destination across multiple networks. It involves the following steps:

1. A host sends a data packet to its default gateway (router) if the destination is not on the same local network.
2. The router examines the destination IP address of the packet and consults its routing table to determine the best path to the destination network.
3. The router forwards the packet to the next-hop router or the final destination based on the routing table entry.
4. If the packet reaches a router that is directly connected to the destination network, it is forwarded to the destination host.
5. If the packet reaches the final destination host, it is processed by the appropriate application or service. Routers use various routing protocols (e.g., OSPF, BGP) to exchange routing information and build their routing tables dynamically.

29. Explain the concept of sharding in databases.

Sharding is a database partitioning technique that involves splitting a large database into smaller, more manageable parts called shards. Each shard is stored on a separate database server instance. Sharding is used to improve scalability, performance, and availability of databases. Some main points about sharding are:

1. Data is distributed across multiple shard servers based on a shard key (e.g., user ID, location).
2. Each shard contains a subset of the data and can be accessed and managed independently.
3. Queries are routed to the appropriate shard based on the shard key.
4. Sharding allows horizontal scaling by adding more shard servers to handle increased data volume and traffic.
5. Sharding can introduce complexity in data management, consistency, and cross-shard operations.
6. Examples of databases that support sharding include MongoDB, Elasticsearch, and Apache Cassandra.

30. Describe the architecture of a modern operating system.

A modern operating system typically follows a layered architecture, consisting of several components working together. The main layers of a modern OS architecture are:

1. Hardware: The physical components of the computer system, including the CPU, memory, storage devices, and peripherals.
2. Kernel: The core component of the OS that manages system resources, provides low-level services, and interacts directly with the hardware.
3. Process management: Scheduling and context switching of processes.
4. Memory management: Allocation and deallocation of memory to processes.
5. File system management: Organization and management of files and directories.
6. Device drivers: Software that enables interaction with hardware devices.
7. System Libraries and Utilities: Provide common functionalities and services to applications, such as input/output operations, network communication, and user management.
8. User Interface: Provides a means for users to interact with the operating system, such as a command-line interface (CLI) or graphical user interface (GUI).
9. Applications: User-level programs that perform specific tasks, running on top of the OS and utilizing its services.

Conclusion

We hope you have gained some insights on Apple Interview Questions through this article. We understand that preparing for interviews can be nerve-wracking and hope these Apple Interview Questions will help you during your interviews and you learn and grow in your role!  

You can also practice coding questions commonly asked in interviews on Coding Ninjas Code360. 

Also, check out some of the Guided Paths on topics such as Data Structure and Algorithms, Competitive Programming, Operating Systems, Computer Networks, DBMS, System Design, etc., as well as some Contests, Test Series, and Interview Experiences curated by top Industry Experts.