Solving complex coding interview questions can be a challenge for many candidates, especially for those who are not familiar with the technical details of the problem. To make the task easier and more efficient, many software developers are turning to state machines to break down the problem into simpler parts and to provide a systematic approach to solving the problem. State machines can provide a way to map out the steps needed to solve a coding interview question, from the initial state to the desired outcome. This blog post will discuss how to use state machines to solve complex coding interview questions, as well as the advantages and potential pitfalls of such an approach. Aspiring coders and seasoned software developers alike can benefit from learning how to break down complex coding problems into simpler parts and use state machines to help solve them.
Getting your act together with State Machines
Making tests for each state of the machine and then testing the transitions between those states would be one approach to unit testing an application that employs finite state machines. Another approach would be to develop tests for each possible event in the machine and then verify that the machine responds to each test by moving to the appropriate state.
A Finite State Machine can indeed be depicted on paper. Making a table with all potential states listed in the left column and all potential inputs listed in the top row will accomplish this. Then, you would record the corresponding output in the table for each combination of state and input.
When the precise behavior of a system is unknown or difficult to predict, non-determinism can be used to model systems with multiple possible behaviors. Additionally, because state machines can be thought of as a series of branching paths rather than a single, linear sequence of states, nondeterminism can make them simpler to design and comprehend.
Automating your tests with finite state machines has a number of benefits. First of all, it can assist in making sure that your tests are thorough and include all potential states and transitions. Second, since the machine will always perform the same steps in the same order, it can help to increase the repeatability and reliability of your tests. Finally, since the machine can run tests much faster than a human can, it can aid in speeding up your testing process.
A key idea in computer science, finite state machines are employed in everything from compilers to network protocols. You may be asked questions about finite state machines during an interview for a job that requires creating or using software. We’ll go over some of the most typical finite state machine interview questions in this article and discuss how to respond to them.
Answer: Let us assume four states such as State a the initial state or reset state. At state b, the value of M is 0 and value N is X (either 0 or 1) At state c, the value of M is 1 and value N is X (either 0 or 1) At state d, assume M has the same value for the last two samples and is 0. At state e, assume M has the same value for the last two samples and is 1. The sequential finite state machine can be drawn for the above state assignment as
The idea is we need to design a complex sequence generator which will detect the patterns 011, 101, 110, and 111. Let us assume four different states a = no 1 detected state. b = one 1 detected state or 01 or 1 detected state. c = two or more than two 1’s detected state. d = 001/010 detected state. The FSM diagram is
Answer: Here, we need to design a complex sequence detector that will detect the patterns 010 and 101. Let us assume four states a = continuous 0’s or no 1 detected state. b = one 1 detected state. c = pattern 10 detected state. d = continuous 1’s detected state. The finite state machine can be drawn as
Answer: Here, the meaning of eliminating the short length pulses is removing 0’s which are between the continuous 1’s and similarly removing 1’s which are between the continuous 0’s. Let us made a 1 after two continuous 0’s as 0, and similarly a 0 after two continuous 1’s as 1. Let us consider four states a = continuous 0’s detected state. b = one 1 in the two 0’s detected state. c = continuous 1’s detected state. d = one 0 in the two 1’s detected state. The finite state machine can be drawn as
Answer: Here, it is required to design an overlapping complex sequence detector that will detect the patterns 0101, 1101, 1010, and 1011. Let us assume four different states a = no 1 detected state. b = at least one 1 detected state. c = the pattern 010 detected state. d = the pattern 1101/0101 detected state. The finite state machine is
What is a State Machine in laymen terms:
Let’s take a look at a very straightforward real-world usage scenario for Uber cab bookings:
Screen 1 is the first screen shown to all users in this use case and is independent. Without providing accurate information on screen 1, you cannot proceed to screen 2. Screen 2 depends on Screen 1. The same is true for screens 3 and 4, which both depend on screens 2 and 3. You remain on screen 4 once your trip is confirmed and neither you nor your driver cancels it. You cannot book another trip until your current one is over.
If a driver declines your trip or is not found in your area to complete it because it is pouring heavily, an error message alerting you to the driver’s unavailability appears, and you remain on screen 3. However, you can go back to screen 2 and then screen 1, or you can go back to the very first screen.
You are going through a different stage of the cab booking process here, and you can only advance to the following stage once a particular action has been successfully completed in the previous stage. Example: If you enter the wrong destination on screen 1, you can’t move to screen 2, and vice versa for screen 3 if you don’t select a travel option on screen 2. However, if your trip hasn’t been booked, you can always go back to the stage where you were before. In the example given above, we have broken down the taxi booking process into a series of activities, where one activity may or may not be able to call another activity depending on where the booking is in the process. This is what state machine is used to model. All of these states/stages should ideally be independent of one another; a stage can only call a stage after it has been completed, either successfully or unsuccessfully.
18 common Google coding interview questions
Make a class that quickly and accurately identifies the Kth largest element in a stream of numbers. The class should have the following two things:.
K. Kth largest number. Example:
Try solving this problem yourself:
Runtime complexity: O(log(K))O(log(K))O(log(K))
Space complexity: O(K)O(K)O(K)
We will use the standard Top ‘K’ Elements pattern to solve this problem. So, rather than using a max-heap, which would be used for the Kth smallest number, we want to use a min-heap. The root is the smallest element in the min heap, as is common knowledge. As we repeat this process for each number, we can compare each one to the root. When a number exceeds root, we will switch the two. When we have iterated through every number, we will then repeat this process.
FAQ
How do you solve a coding problem interview question?
- Visualize the problem by drawing it out …
- Think about how you would solve the problem by hand .
- Come up with more examples …
- Break the question down into smaller independent parts …
- Apply common data structures and algorithms at the problem
How do you write a code for a state machine?
- Identify initial state. Determine the initial state of your application when it is a finished product before you start writing any code.
- Identify events. Events are what prompt an application to transition from one state to another.
- Determine transition.
What is state machine coding?
State machines are a type of programming architecture that allow states to flow dynamically based on values from earlier states or user inputs. Applications that fit this description of an architecture include a combination of: Logic for making decisions about when to relocate to a specific state
What is state machine with example?
Many real-world systems can be thought of as state machines. For example, computer processors are state machines. They receive signals from outside the chip, modify some on-chip state, and respond by producing outputs. The possible states for the processor chip are limited to a small number.
