Difference Between Stack and Array
Have you ever wondered about the difference between a stack and an array? A stack is a LIFO (Last In, First Out) structure, allowing only top-element operations, whereas an array offers indexed access to its elements, supporting a wide range of actions like direct retrieval, insertion, and deletion at any position. Let's understand more!
A stack is a linear data structure that operates on the Last In, First Out (LIFO) principle, where the last element added is the first to be removed, typically featuring operations like push, pop, and peek. On the other hand, an array is a collection of elements, each identified by an index, allowing direct and random access to any element. In this blog, we will see the differences between them.
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Difference Between Stack and Array
Below is a table highlighting the differences between Stack and Array.
| Criteria |
Stacks |
Arrays |
| Conceptual Definition |
A stack is a sequential structure operating on a LIFO basis, meaning elements are added and removed from one end ('top'). |
An array is a sequential collection of elements, with each element identified by a numerical index. |
| Operational Principle |
Adheres to LIFO, where the most recently added element is the first to be removed. |
Offers indexed positioning, allowing direct retrieval of any element via its index. |
| Modification Methods |
Supports operations like 'push' for adding and 'pop' for removing elements, exclusively at the top end. |
Permits insertions and deletions at any position, with the ease varying based on the array type (static or dynamic). |
| Size Flexibility |
Typically resizable, especially in implementations using linked lists, but array-based stacks have fixed size. |
Primarily fixed in size, however, dynamic array structures like vectors can adjust size as needed. |
| Uniformity of Elements |
Generally homogeneous in data type, although implementations can vary. |
Composed of elements of a consistent data type for uniformity and memory efficiency. |
| Search Capability |
Limited to linear search due to its sequential nature. |
Supports both linear and binary searches, with binary search applicable in sorted arrays. |
| Element Accessibility |
Restricts access to the top element only, in keeping with the stack protocol. |
Enables immediate access to any element using its unique index. |
| Structural Foundation |
It can be structured using other data types like arrays or linked lists. |
A foundational data structure, not derived from stacks, and integral to most programming languages. |
| Range of Operations |
Characterized by a limited set of specific operations, such as push, pop, and peek. |
Exhibits a broad spectrum of operations, including sorting, searching, updating individual elements, etc. |
| Pointer Utilization |
Typically uses a singular pointer (top) to mark the latest element in the stack. |
Utilizes indexed addressing for elements, with memory allocation either static (defined at compile-time) or dynamic. |
What is a Stack?
A stack is a fundamental data structure used in computer science. It operates on the Last In, First Out (LIFO) principle, where the last element added to the stack is the first one to be removed.
Characteristics of a Stack
1. LIFO Principle: In a stack, the most recently added element is the one that is removed first. This is akin to a stack of plates; you take off the top plate (the most recently added) first.
2. Operations
- Push: Adds an element to the top of the stack.
- Pop: Removes the element from the top of the stack.
- Peek (or Top): Returns the element at the top of the stack without removing it.
- isEmpty: Checks if the stack is empty.
3. Usage: Stacks are used in various applications such as reversing a word, undo mechanisms in software, backtracking algorithms, and managing function calls (call stack) in most programming languages.
4. Implementation: Stacks can be implemented using arrays, linked lists, or other data structures. The choice of implementation affects the efficiency of stack operations.
5. Efficiency: The basic operations (push, pop, and peek) generally have a time complexity of O(1), meaning they are performed in constant time.
6. Limitations: One of the main limitations of a stack is that it does not allow random access to the elements. You can only access the top element at any given time.
Example Showing Usage of Stack
Problem Statement: Balanced Parentheses Check
Suppose we need to write a program to check whether an expression has balanced parentheses. An expression is said to have balanced parentheses if each opening parenthesis "(" has a corresponding closing parenthesis ")" and the pairs of parentheses are properly nested.
For example
- "((a + b) * c)" is balanced.
- "(a + b))" is not balanced.
We can use a stack to tackle this problem efficiently.
#include <iostream>#include <stack>using namespace std;
// Function to check if parentheses are balancedbool areParenthesesBalanced(string expr) { stack<char> s; char x;
// Traversing the Expression for (int i = 0; i < expr.length(); i++) { if (expr[i] == '(') { // Push the element in the stack s.push(expr[i]); continue; }
// If current character is not opening parenthesis, then it must be closing. // So stack cannot be empty at this point. if (s.empty()) return false;
switch (expr[i]) { case ')': // Check the top element of stack. If it's an opening parenthesis, pop it. x = s.top(); s.pop(); if (x != '(') return false; break; } }
// Check Empty Stack return (s.empty());}
int main() { string expr = "((a + b) * c)"; if (areParenthesesBalanced(expr)) cout << "Balanced\n"; else cout << "Not Balanced\n"; return 0;}
Output
Balanced
What is an Array?
An array is a fundamental data structure in programming that consists of a collection of elements, each identified by an array index. Arrays store multiple items of the same data type in a contiguous block of memory.
Characteristics of an Array
1. Fixed Size and Homogeneous: An array typically has a fixed number of elements (its size is defined at the time of creation), and all elements must be of the same data type (like all integers, all floats, etc.).
2. Indexed Access: Each element in an array is accessed by an index. Array indexing usually starts from 0, meaning the first element of the array is at index 0, the second element is at index 1, and so on.
3. Efficient Element Access and Iteration: Arrays allow efficient access to elements as they can be directly accessed using their index. This makes arrays particularly useful for iteration and quick element access.
4. Memory Allocation: In memory, an array is allocated as a contiguous block. This means that the elements of the array are stored in consecutive memory locations, which allows for efficient access patterns due to spatial locality.
5. Use Cases: Arrays are used in various programming scenarios, such as storing data that needs to be accessed sequentially or via an index, in algorithms that require random access to elements, and in scenarios where the number of elements is known beforehand.
6. Static vs Dynamic Arrays: In some programming languages, arrays have a static size, meaning their size cannot change once allocated. Other languages support dynamic arrays (like vectors in C++ or lists in Python) that can resize themselves when needed.
7. Multi-Dimensional Arrays: Arrays can be more than one-dimensional. For example, two-dimensional arrays (like a grid or matrix) are commonly used in applications that require a tabular data representation.
Example Showing Usage of Array
Problem Statement: Find the Maximum Element in an Array
Suppose we need to write a program that finds the maximum element in an array of integers. The array contains a list of numbers, and we want to identify the largest number among them.
#include <iostream>using namespace std;
int findMaximum(int arr[], int size) { int max = arr[0]; // Assume first element is the maximum initially
// Iterate through the array for (int i = 1; i < size; i++) { if (arr[i] > max) { max = arr[i]; // Update max if a larger element is found } }
return max;}
int main() { int myArray[] = {3, 10, 4, 7, 15, 2}; int size = sizeof(myArray) / sizeof(myArray[0]);
int maxElement = findMaximum(myArray, size);
cout << "The maximum element in the array is: " << maxElement << endl;
return 0;}
Output
The maximum element in the array is: 15
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Conclusion
Thus, arrays and stacks are distinct data structures in computer programming, each serving different purposes and offering unique functionalities.
FAQs
What is a stack, and how does it differ from an array?
A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle, where the last element added is the first one to be removed. An array, on the other hand, is a data structure that stores a fixed-size collection of elements, and elements can be accessed by their index.
How are elements added and removed in a stack compared to an array?
In a stack, elements are typically pushed onto the top of the stack using the "push" operation and popped from the top using the "pop" operation. In an array, elements can be inserted at any valid index and removed by setting the element at a specific index to a null or default value.
What are the advantages of using an array over a stack, and vice versa?
Arrays are advantageous when you need direct access to elements by their index and when the size of the collection is known in advance and remains constant. Stacks are advantageous when you need to manage elements in a last-in-first-out order, such as in function call execution or expression evaluation.
Can a stack be implemented using an array, and vice versa?
Yes, it is possible to implement a stack using an array by restricting the operations to push and pop only from one end (usually the end with the highest index). Conversely, an array can be used to implement a stack-like structure by managing the index at which elements are added and removed.
What are the memory and time complexity differences between arrays and stacks?
Arrays have constant-time (O(1)) access to elements by index but may have a time complexity of O(n) for insertions or deletions if elements need to be shifted. Stacks have O(1) time complexity for push and pop operations. In terms of memory, stacks tend to use memory more efficiently as they only need to store the elements themselves, whereas arrays may require extra space for potential future elements.
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