Link to the video: SkillYaan | Stacks
Link to the code on stacks in Java: SkillYaan | Stack Demo | Java
This article provides a comprehensive overview of stacks, a popular data structure used in computer science.
It explains -
What a stack is
How it is implemented
The operations that can be performed on it, including push, pop, and peek.
The article also highlights the various applications of stacks in engineering, such as memory management, compiler design, operating systems, networking, and graphics and image processing.
Finally, the article lists some common interview questions related to stacks and offers tips for preparing for them.
If you are looking to learn more about stacks and their practical applications, this article is a great resource to get you started!
Source: HackerEarth
A stack is a fundamental, linear data structure in computer science that stores a collection of elements and operates on the principle of Last-In-First-Out (LIFO). In a stack, elements are inserted and removed only from one end, known as the top of the stack. The other end of the stack is called the base.
The stack is a simple data structure that can be implemented using an array or a linked list. A stack using an array would typically have a fixed size, whereas a stack implemented using a linked list can grow dynamically based on the number of elements it contains.
The primary operations performed on a stack are push, pop, and peek. The push operation adds an element to the top of the stack, the pop operation removes the top element from the stack, and the peek operation returns the top element without removing it.
Here, visualize it: https://www.cs.usfca.edu/~galles/visualization/StackArray.html
A stack can be used in a variety of scenarios, some of which include:
Reversing the order of a set of elements.
Checking for balanced parentheses in an expression.
Tracking the state of a program during function calls.
Evaluating expressions in postfix notation.
Undo and redo operations in text editors.
Real-life examples of stacks can be seen in various applications, such as the undo and redo feature in text editors, the use of back and forward buttons in web browsers, and the call stack used in programming languages like Java, Python, and C++.
Stacks have various applications in engineering. Here are a few examples:
Memory Management: Stacks are widely used in memory management, especially in embedded systems. For example, when a microcontroller executes a subroutine, it stores the return address in a stack. When the subroutine finishes executing, the return address is popped from the stack to return control to the main program.
Compiler Design: Stacks are used in the design and implementation of compilers. The compiler uses a stack to keep track of the control flow of the program during the parsing and evaluation of expressions.
Operating Systems: Stacks are used in operating systems for process and thread management. Each process has its own stack, which is used to store the execution context of the process, including the values of local variables and the return address of function calls.
Networking: Stacks are also used in networking protocols like the Transmission Control Protocol/Internet Protocol (TCP/IP) stack. The TCP/IP stack uses a stack of protocol layers to handle communication between computers over a network.
Graphics and Image Processing: Stacks are used in image processing and graphics applications to implement undo and redo functionality. Each step in the image processing or graphics operation is pushed onto a stack, and the undo operation pops the most recent step from the stack.
These are just a few examples of how stacks are used in engineering. Stacks are versatile data structures that can be used in various applications, from embedded systems to networking protocols and image processing.
Both Java and C++ have implementations of the stack data structure in their respective Collections Framework and Standard Template Library (STL):
In Java, the stack data structure is implemented as a class called Stack in the java.util package. The Stack class is a subclass of the Vector class and provides methods such as push(), pop(), and peek() for adding, removing, and accessing elements in the stack.
Here is an example of how to create and use a Stack in Java:
In C++, the stack data structure is implemented as a container adapter class called stack in the STL. The stack class is implemented using a deque (double-ended queue) by default, but it can also be implemented using a vector or a list. The stack class provides methods such as push(), pop(), and top() for adding, removing, and accessing elements in the stack.
Here is an example of how to create and use a stack in C++:
In both Java and C++, the stack data structure is a useful tool for solving a wide range of problems.
In Java, the Stack class provides two useful methods for querying the status of a stack: size() and empty().
The size() method returns the number of elements in the stack. It does not modify the stack and can be called at any time. If the stack is empty, size() will return 0. Here is an example of how to use the size() method:
This will output: The stack has 3 elements.
The empty() method returns a boolean value indicating whether the stack is empty. It can be used to check if the stack is empty before calling the pop() method to avoid a NoSuchElementException. Here is an example of how to use the empty() method:
This will output: The stack is empty.
Both the size() and empty() methods are simple but useful methods for working with stacks in Java. By using these methods, you can easily check the status of a stack before performing any operations on it, which can help you avoid errors and improve the overall robustness of your code.
Did you know that recursion can be implemented using stacks?
In fact, most programming languages implement function calls using a call stack, which is a stack data structure used to store information about the active subroutines and functions of a program.
When a function is called, the system pushes the return address and other relevant information onto the call stack, and when the function returns, the system pops this information from the stack to resume execution at the point where the function was called.
This implementation of recursion using a stack is called the iterative approach, where each recursive call is replaced by a loop that performs the same operations using a stack. This approach can be more efficient than the traditional recursive approach, as it avoids the overhead of maintaining a separate stack frame for each recursive call, which can be significant for deep recursion.
Let us look at some must do interview/exam questions,
What is a stack, and how is it implemented?
What are the operations performed on a stack, and what is their time complexity?
What is the difference between a stack and a queue?
How is a stack used in memory management in embedded systems?
Explain the use of a stack in the implementation of compilers.
What is a call stack, and how is it used in programming languages like Java, Python, and C++?
How is a stack used in operating systems for process and thread management?
What is a TCP/IP stack, and how is it used in networking protocols?
Explain how a stack can be used to implement the undo and redo functionality in graphics and image processing applications.
What are the advantages and disadvantages of using an array-based implementation versus a linked list-based implementation for a stack?
These questions cover various aspects of stacks, including their implementation, operations, and use cases in different applications. Be sure to prepare for these questions before your engineering interview.
Most important coding interview questions on Stack for product-based companies: -
2. 0/1 Matrix
Answers to some questions that were left unanswered earlier:
What is a stack, and how is it implemented?
A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle, which means that the last element added to the stack is the first one to be removed. Stacks can be implemented using arrays or linked lists. In an array-based implementation, a fixed-size array is used to store the elements, and a variable called top is used to keep track of the index of the last element added. In a linked list-based implementation, each node of the linked list contains an element and a pointer to the next node.
What is the difference between a stack and a queue?
A stack and a queue are both linear data structures, but they differ in the way elements are added and removed. In a stack, elements are added and removed from the top of the stack, while in a queue, elements are added at the rear and removed from the front. Another key difference is the order in which elements are removed from the data structure. In a stack, the last element added is the first one to be removed (LIFO), while in a queue, the first element added is the first one to be removed (FIFO).
Explain the use of a stack in the implementation of compilers.
Compilers use a stack to keep track of the control flow of the program during the parsing and evaluation of expressions. When the compiler encounters an opening parenthesis, it pushes it onto the stack. When it encounters a closing parenthesis, it pops the stack to find the corresponding opening parenthesis. This ensures that the expressions are evaluated in the correct order, according to the rules of operator precedence and associativity.
How is a stack used in operating systems for process and thread management?
In operating systems, each process has its own stack, which is used to store the execution context of the process, including the values of local variables and the return address of function calls. When a process makes a function call, the return address is pushed onto the stack. When the function returns, the return address is popped from the stack to return control to the calling function.
Explain how a stack can be used to implement the undo and redo functionality in graphics and image processing applications.
In graphics and image processing applications, each step in the operation is pushed onto a stack, and the undo operation pops the most recent step from the stack to undo the operation. The redo operation can be implemented by pushing the undone operation onto a redo stack. When the user requests a redo operation, the most recent operation on the redo stack is popped and performed.
An array, array list, and stack are all data structures that store a collection of elements. However, there are some key differences between them:
Array: An array is a fixed-size data structure that stores elements of the same data type in contiguous memory locations. Elements can be accessed using their index position, and the size of the array cannot be changed once it is created.
ArrayList: An ArrayList is a dynamic array that can grow or shrink in size as elements are added or removed. It stores elements of the same data type in contiguous memory locations, similar to an array. However, an ArrayList is implemented using a dynamic array and provides methods for adding, removing, and accessing elements at any position in the list.
Stack: A stack is a data structure that follows the Last-In-First-Out (LIFO) principle, which means that the last element added to the stack is the first one to be removed. It stores elements of the same data type and can be implemented using an array or a linked list. In a stack, elements are added and removed from the top of the stack.
If you want to learn more about stacks, there are many resources available online.
A good place to start would be -Topcoder (Data Structures (topcoder.com))
Whether you're working with embedded systems, compilers, networking protocols, or image-processing applications, mastering stacks is a crucial part of your toolkit.
So keep on stacking and don't let your functions overflow!
“Why did the stack overflow? Because it had too many functions calls on the stack!”
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